The "Stereo-wave" experiment: A contribution of Rijkswaterstaat and the Delft University of Technology to JONSWAP 2

\

~rhe ~_!_~t__ee_O_-_~l_.'l_V_C_Il! __ ~ __

A contribution of Rijkswaterstaat and

the Delft Uni.ver sity of Technology to

I

JONS\.lAP 2. I Iprogress report

I.

I December 1972

Vloeistofmechanica

Afd. Weg- en Waterbouwkunde

Technische Hogeschool Delft

R/1973/2/L L.H. Hoithuijsen The "Stereo-wave" experiment.

A contribution of Rijkswaterstaat and

,

the Del

ft

Univer

sity of

Techn

ology to

JO

N

SWAP

·2.

December 1972 _{ir. L.H. Holthuijsen} Preface

This report is intended to give a brief description of the ideas underlying the experiment of RWSx and THDxTn the framework of JONSWAP 2 and the practical implications thereof.

Some results of the preparation of this experiment are given. It is tried to explain some of the theoretical concepts in a simple manner.

x Rijkswaterstaat (RWS)

Contents

page

I Introduction.

11 Set-up of JON SWAP 2. 111 The seawave spectrum.

IV The stereophotogrammetric procedures V Camera synchronization. VI Airplanes. VII Conclusion. VIII References. IX Appendices. 3 9 11 20

23

25

26

-1-1 Introduction

In order to predict seawaves from atmospheric data, some under -standing of generation and attenuation of seawaves is necessary. During the last 25 years some theories on wave generation have been developed and a fairly adequate way of describing the waves has been found. Fieldstudies in context with theories of generation and

attenuation have been realized only a few times. One very important experiment, during which the energy balance of the waves was obtained, has been carried out in the North Sea in 1969: the Joint North Sea Wave Project (JONSWAP).

During this project it appeared that an even more detailed study would be needed to determine the energy transfer from wind to water.

Above that it appeared that the assumptions about wave attenuation were not correct and a different approach to this problem would beo needed. Therefore it was decided to have a similar experiment with more emphasis on energy transfer and wave attenuation.

In September 1973 a group of oceanographic institutions from several countries (Canada, Denmark, France, Germany, Holland and the United States, see App. I) will carry out this second project

(JONSWAP 2). Near the coast of the German Island of Sylt measurements

,

will be carried out on wind- and wave characteristics in a line

(length about 60 km) perpendicular to the coast. The stations in this line consist of piles, buoys and ships. During some situations,

measurements will also be executed from airplanes.

One of the most adequate ways of describing the waves is:presenting the distribution of the energy according to wavelength and wavedirection (the directional spectrum). Information about the direction of the waves will be obtained to some extent from a particular type of buoy

and from a combination of piles.

A more precise measurement of the direction of the waves will be carried out from airplanes: laser-altimeters and stereophotography.

-2-Non-directional information of the waves will be obtained by a large number of sensors.

Knowledge about the directional spectrum is needed not only for wave prediction but also for the determination of forces on ships, oil-rigs etc. Up till now this directional spectrum has been measured only a few times and a new measurement with such a operatio-nal and theoretical background as created by JONSWAP 2 would be most welcome.

The Delft University of Technology and the Rijkswaterstaat wished to contribute to JONSWAP 2 by realizing a measurement the result of which should be some directional spectra (preferably as a function of fetch). The experiment ean be carried out by using ste-reophotography. This is a rather complicated technique but it allows us not only to obtain wavespectra but it allows us toa to study wave behaviour near the coast and near constructions (piers, harbours etc). As Ri jk swater staat is concerned with these waves toa, this was an extra motive to ask their survey department to carry out the photo-grammetric procedures. This department has same experience with

stereophotography of waterwaves: in 1958 a basically identical procedure was used near the Dutch coast and quite recently attempts have been made to use this methad in a hydraulic laboratory.

Presently stereopictures of seawaves are being made from a helicopter. The experiments have been encouraging but adaptations will be neces-sary for the experiment at hand.

The experiment is supported by the Direktie \<laterhuishouding en \oJaterbeweging,the Delta Dienst and the Meetkundige Dienst of Rijkswaterstaat and the Afdeling der Weg- en Waterbouwkunde and the Centrale Elektronische Dienst of the Delft University of Technology.

-3-11 Set-up of JONSWAP 2

A number of oceanographic instvutions will try to study the wave development while energy is added (by the vlind) or drained (dissipation). It is desirable for such a study to have one large group of institutions for one large experiment (rather than having each institute conduct its own, uncorrelated experiment). In 1969 it was shown that such a cooperative realization of a large experiment is feasible (JONSWAP, ref I). During JONSWAP 2 the organization is basically the same: each institute contributes to tne experiment while these contributions are coordinated by a central "brain". By this, each institute can concentrate on its own measurement(s).

One of the main features of the project 1S to obtain an insight in the energy balance of the wavespectrum. A substantial contribution to

the theoiy concerning this~balance has been given by Hasselmann (reL 7). JONSYlAP2 is initiated mainly by this scientist and the theoretical aspects concerning the core program will be hand led chiefly by him. The op~rational coordination will be carried out by the Deutsches Hydrographisches Institut in Hamburg. These people will take care of the accommodation, logistics and local facilities (wave-piles,

telemetry, computer etc.). No formal organization has been built and the whol,ecooperation is bas ed on voluntary and informal contacts • In spite of this, financial support for organizing the project has been obtained from national and international bodies. The realizations of the individual experiments have to be funded by the participating institutions: each institution sees to it that its own delegation is supplied with sufficient financial and material support to carry out its experiment. As to the equipment: the participants should he totally self-supporting (except for the local facilities). This way of data-collecting will cause some interface problems but by proper arrangements beforehand, these problems may be minimized.

The tvo main problems which will be investigated by JONS~.JAP2 are

wave generation and wave attenuation. The study of wave generation will be focused up on the energy fluxes of the atmosphere to the waves and smong the wave components mutually. The wave attenuation will be studied by observing the decrease of swe lI on appr oachi.ng the coast.

-4-A review of the scientific objectives 1S given in App. 11. The measure-ments will be devoted to:

wave generation: mechanism of energy transfer from atmosphere to waves. coupling of waves.

energy dissipation at short wavelengths. energy balance of the wave spectrum.

influence of the wi.nd gustine ss on the spectral development.

wave attenuation: influence of bottom irregularities on the observed decrease of swell in shallow water.

This list of problems is the "core" of JONSWAP 2. Because of the advánced level of this project a number of institutions thought it interesting and convenient to participate with ~other experiments.

These measurements are concerned with:

relationship between radar-backscatter and the highfrequency part of the seawave spec trum (including an investigation of the interactions of short and long waves).

investigation of the IIplanetaryboundary layerll (the first few hundred meters of the atmosphere). measurements of heat-flux near the wat er+a tmosphere boundary.

The measurements which are needed to investigàte all these problems ,'lillbe devoted to (see App, lIl):

atmospheric pressure wind velocity watersurface movements air temperature air humidity wa ter temperature.• currents radar-backscatter heat flux humidity flux

-5-Some of the instrumentation to measure this still has to be developed.

The carriers for the equipment will be provided by the institutions themselves or by the coordination of JONSWAP 2. So several types of carriers will be available: piles, buoys, ships and airplanes.

=

Wave generation by wind (operational).

=

The most important objective of JONSWAP 2 is to find a theoretical model which may help us to predict waves at sea from atmospheric data.

Of crucial importance to this is the generation of waves by wind. The generated wave energy will depend mainly upon the windvelocity, the d u-ration of the wind and, more or less equivalent, the fetch of the wind. During JONSWAP 2 the attention will be concentrated up on the dependenee of duration and fetch (preferably during several wind eenditions). Onee the relations spectrum-fetch and spectrum-duration are known for

the values near Sylt, it is possible to generalize these relationships. Evidently it.is necessary to have a defined fetch. The most simple situation for this is a sharp boundary where the wind starts to act on the water: the coast with an off-shore wind. If we take it that the coast is straight and infinitely long and that the wind does not change along the coast, w~ may neglect the variations of the spectrum along the coast.

I

I

-6-When we have a look at the map (App. IV and V), we see that the coast of Sylt is rather long and straight. Besides this the bottom meets the condition; no influence on wave generation.

-

11 ..

The coast is orientated westerly

(28t'

to be exact). Situations with an off-shore wind can be expected to occur several times during the

month of September near Sylt. The meteorological situation then is rather persistent (high pressure area over Finland-Russia, low pressure area near the Britisch Isles (App. VI»)and the wind may be constant for one day or more in strength and directlon.

-- Decrease of swell on approaching the coast (operational).

=

=

An important question in wave prediction'is: what happens to the waves once they have left their generation area? It is expected that

the energy of the waves will decrease. This may be due to energy trans-fer to heat or currents, energy dissipation through counterwinds, battom friction etc•• JONSWAP 2 will be concerned with one of these aspects: the influence of the bot tem. As the influence of the bot tom is negli-gible during the wave generation cases, we wil1 need other conditions to study this LnfIuence, Long waves \-7i11"fee l" the bottom. Preferably waves wMth have left their area of birth: swell approaching Sylt. In order to avoid complex refraction effects this swell should enter the Sylt area from one direction and more or less perpendicular to the coast. It is rather common for Sylt to have this swel1 (not refracted by the Dogger Bank, coming from the West). Again the wave char~cteristics vary perpendicular to the coast and not a10ng the coast.

-7

-=

Locations of the stations. a

It is obvious that the dependenee of wave characteristics on the distance from the coast is the most important feature for JONSWAP 2.

There are several methods to obtain the relationships:

1. While travèling along with one wavecomponent, we can measure its

energy content (ref. 24). A great drawback is that we can investigate the properties of only ane component at a time, during one run. The

proper ties of other components may be recorded during other runs but this is time-consuming. For investigating the interactions between the components this method might get very complex.

2. A series of stations and recordings situated at proper locations and times may avo i.dmost of the drawbacks of l, This technique has been tried in 1968 during a pilot experiment for JONSWAP but this proved to require a coordinàtion of instruments, people and weatherforecasts

which could not be realized.

Continuous recording at a series of stations during a long period of time may be chosen. This has been done in 1969 and it will be used

again in September 1973: the larger part of the wind- and wave sensors will operate every two hours (length of one record ~-1 hour). Some of

the recording equipment though will operate only during favourable con -ditions (airplanes, fragile instruments).

In case of an ideal wind and coast, the .Locat i.ons of the sensors

may be choscn at random along the coast (at prescribed distances from

the coast). To minimize the influence from the sides in case of Sylt , the stations will be situated more or less in ane Line, During JONSvlAP2

this line will have a length of 62 km. Per station several observations

will be made. Sometimes several instruments at one station wi ll, record

one and the same variable. This is done in order to have an inte

r-camparison of the performance of several types of instruments used in the array. To obtain an idea of the influences from the sides and to be able to record the atmospheric conditions properly several stations are located out of the line:

..

.

'"

-8

-The labeling of the stations is a heritage of JONS\JAP.

station

o

4 S

Sa

Sb

7 8

8

a Sb 9 10

io"

10D

I

O

c

10' 11 and 12 W

=

wind I. .'" < '0 distance from shore

km

variable

H,

T

W,T

WA

W,T,p,HF,R,\vA W

20

27

W,WA

WA

37

52

1>1A,W,P, C , R WA,W

WA,

H

WA

,W

WA,W W W W W

62

not occupied T "" temperature \JA '"waves

p

..

atmospheric pressure

HF

== heat flux

R

_""

infrared radiative séasurface temperature C

_'"

current instrument carrier tower pile buoy piLe & wavef o Ll ove r buoy buoy buoy \ p~le

&

wavefollower buoy buoy buoy buoy buoy buoy buoy buoy

-9-The instruments near stations 8, 8a and 5 need a continuous survey

and therefore severa1 ships are anchored near these stations (station 5: two ships; station 8: five ships; station 8a: one ship).

The registrations from ~he airplanes wi11 be obtained by using (stereo-) photography, laser-altimeters, radar and windsensors. The aircrafts will collect their data along the array (these loeations do not necessarily have to coincide with the ground stations). They will operate from an airfield at Sylt and probably fDom other German or Dutch airfields.

111 The seawave spectrum.

Consider a registracion of the watersurface elevation (measured for instanee by a wave pole):

'!

~>

t

This is a very irregular function (of time) but we may thiPkof it as being composed of a large number of sine- and eosine waves (wave com-ponents). Each component then will have a frequency, a phase and an amplitude. Usually we look at the energy of the waves. This energy is proportional to (amplitude)2. Presenting the energy density as a funetion of frequency, we obtain the energy epectrum S(f):

f

.\0 -t.+...-\'

The definition is such that the area of the spectrum between f and

o

between f

o

to the energy carried by the wavecomponents

f +[;f is equal o and f +6f. It is a o For describing the "smooth" function ~n case of windwaves.

waves and related processes, this concept of the

-10-The form of the spectrum is known for quite some time. During JONSWAP,

the energy balance of the spectrum was determined (which components are getting energy from the wind, hO\'1 much energy is transferred from one com

-ponent to the other, where is energy dissipated):

The seasurface is not fully described by the movements of the wate r-surface at one point (our wavepole). The spatial information is lacking.

If we could freeze the sea at one instant, we would have a surface vh Lch

looks just as irregular as the registration by the wave pole, only in

two dimensions. We could again think of this surface as being the sum of

a large number of components in many directions:

-11- .

Instead of having the energy density as a function of frequency, we now

have the energy density as a function of waveLeng th and direction (thc direc+

tional spectrum). Or rathcr a function of thc reciproke of the wavelength

and thc direction:

This function has been determined on1y a few times (App. VII). Thc aim of the "Stereo-wave" experiment is to obtain directiona1 spectra in the fréU-ne -work of JONSWAP, 2.

From now on in this report,for convenience sake,the spectra which are a function of wavelength and direction are j.rescut.ed one-dimensionally. The reciproke of the wave1ength is called wavenumber: k

=

lIL (in analogy

with frequency f

=

1

/

)

period'

IV The stcreophotogrammetric procedure.

,From the preceding pages it may be deduced that the most obvious method to determine the 2D-spectrum is fourier transformation of a spatial

registration of the seasurface. This however is a very complex methad and it is of ten tried ta approach this spectrum in other ways;

a. A group of piles or pressure gauges (ref. 18). In general the direc-tional resolution is rather limited because of the restricted number of sensors. The computations are time-consuming.

b. Measurement of the watersurface elevation and gradiertt (ref 13). This may be done by a buoy equiped with accelerometers. The directional res

o-lution again is limited while the practical use is problematic. c. By Itcutting"the surface in several directions; for instanee by carrying out accurate altitude measurements from an airplane which is flying a pattern (ref. 19).

There are still other methods (same will be investigated during JONSWAP 2)

sueh as radar-backscatter and other, optical methods (ref. 8 and 11).

The most accurate method at this moment seems to be tbe spatial

registration of the seasurface by stereophotography. 'Ihis method has been

used to obtain some of thc existing approximations of the 2D spectra. At

-12-Canada: Lake Winipeg 1969 (ref.lO).

France: Algiers (1933) from land; France (1945 and later) from airplanes

(ref. 6, ref. 15). Germany: 1904-1925 from ships (ref. 20).

Holland: 1958 from jet-airplanes (ref. 16).

U.S.A.: SWOP land SWOP 11 in 1954 and 1967, from airplanes (ref. 5 and 21). U.S.S.R;:1907 and 1931 Black Sea; 1946-J9507 (ref. 14 and 12).

Of these experiments the first .and last two have given spectra. The results of the Russian experiments are hard to come by. The Canadian experiment has been a rather rough approach. The measurements in the United States seem to have been the most successful and in fact a substantial part of our empirical knowledge of the spatial seawave spectrum comes from t~ese experiments.

The SWOP I report has given us valuable information for the realization of our experiment, whi ch is very similar to SWOP.

=

The basic idea of stereophotography.

=

The perception of a spatial image by a human being is based upon a very complex processing of visual inf·ormation. The sensing and processing is done by the eyes and the brains (size, colour, stereoscopy, perspective etc). In stereophotogrammetry the 3D perception of the eyes is used~ This appreciation of depth is mainly achieved by, what is called, stereo-scopy,(other phenomena will not be considered now). Stereoscopy is not fully

understood but it is known that it is based upon interpretation of parallax measurements by the eyes. When we look at an "object, usually a slightIy different Lmage is given to our left and right eye. This difference is caused by the fact that the position of each of the eyes relative to the object is different. A certain point in the image of the Ieft eye will be shifted relatively in the image of the right eye. This sketsch

,

,p, C. I, a,

I

'

~

-

'

-

-.

- - /.'.

.

.

,

}'.' ~

,

.

"..

"/' 'I , "','''.

"P

.

,,

'

I " I , ( .... .1 1 I " j I I 1. I " '

,

'

:

'

(' " 'f .-, • -1 3-2. I 1 front V1.ew I f , 1 I 1 ,., ,'" I , i, I, , _,I - ---pyramid pointing forward

V1.ew from above

The points A' '-A',

B'

I-

B

'

and C' '-C' will be interpreted as belonging to one plane as there mutual position did nog change. The points P"_P'

though wil! be interpreted as a point in front of the ABC-plane. The shifting of p"_p is conveniently cal led parallax.

By offering to the eyes two photographs of an object which has been phot o-graphed from two positions, a

3D

i1lu5ion ean be obtained. The left eye

is offered the left picture and the rigth eye the rigth picture. By the

image interpretation

the

brains regist::rs

a 3D

space. This

is

used in

stereo-phouogr ananetry , The coo cdinate s of points in the simulated 3D space are measur ed by compar i.ng(by the human eye) depth with a reference depth.

This comparison is achieved by moving a mark mechanically on the tvlO

photographs; the eyes interpret these movements as a point "floatingll

in spuce. By identifying (hand control) this point with the point that

shou Id be measur ed, the x, y and z coordina tes Cll11 be registred from the

coordinates of the reference mark on the two photograplls. Assuming vertical

=

Stereophotography of waterwave s and its analysis =

In order to sce a

3D

object in the simulated space, the object must be visible: identifiable points should be available to obtain stereoscopy. In this respect several probleros are to be expected when recording

water-a. Introduction of false parallax by movement of the object. During the foregoing considerations it was assumed that the object did not change shape ofdid not move during and between the t"10exposures, if these are not made simultaneously. If these movements occur the result woul d be an introduction of false parallax which is interpreted by thc eyes as an extra, and th~refore incorrect lefeldifference. Usually the pictures are obtained by photographing a non-moving object with oné camera from different

posi-tions. For instanee one airplane equiped with one camera which is triggered at a few seconds interval.

In case of a rooving nn/or reshaping object the interval between the exposures

should be very short to

limit

the displacernents of thc object. In our

si.tuation the distance between thc camera positions should be same hundreds

of meters. waves: -)4-.,\;çç~te",l:; ..'t;",~, c1\" .!!. J.~ b·Ç

1

t rof... "

fJ...

A ?&/Io =

't

.,

-1

5-This implies a very fast moving camera, which is impractical. Therefore it

is better to use two cameras. Thc cameras should be trigp,eredsimulataneously

and with a very short exposure time. In practice of course the synchronization

is not perfect. The limitations for the acceptable synchronization error

are hard to find. Ey using the experiences of the experiments in France

x

and the United States and by own judgemcnt t.he-cconc Iusion was.;

the synchronization should be better than 1 ms. During SWOP some exposures

were studied having 5 ms but this still seemed to be acceptable

b. The existence of identifiable points on the watersurface. In particu

-lar thc laboratory experiment (ref 9) showed this problem: the waves.were

very smooth and transparent. No stereoscopy could be obtained on this s

ur-face. Only by applying a thin layer with a very definite "pattern" stereos

-copy could be achieved (aluminium powder was used)« The same problem can

be met oVer sea: smooth waves will not be visible in the sense of stereoscopie

perception. The only "solution" here is to hope for a substructure on the

waves caused by wind (small ripples), foam, dirt etc.

c. Parts of the picture which are exposed incorrectly will not give suf

fi-eient information to be interpreted. Especially sunreflection on the sea

-surface and eloud shadow'

wi

ll b

e

hazardous.

d , Wrong interpretation of sun-glitter. During the anal.ysis of the

photogra hs, the parallax of a point in the physical model is measured.

If there are points in the exposures, which, by mi.stake , are interpreted as

the images of this point, tnen an incorrect elevation

is

obtained.

In

parti

-cular the facets of the watersurface which rcfleet the sun to the cameras

could have this effect. 'I'he points A and B may be interpreted as C. l-nlether

this will give practical p~oblems during the analysis of the photographs

is not knovn.

x \.Javes of peri.od5s have a velocity of about 7n/s, th c r ate of te shapi.ug

of the sc asurfac e may be of order 5 mis. In I ms rhi s imp Li.es a horizontal

displacement of 5 mrn, whi.chis just acceptab Le from a phot.o grammetric

-16-Apart from the problems a-d, which are inherent to stereophotogrammetry, we have to deal vith problems concerning the analysis of the registratiou. These problems ~vill be encountered na t only in stereophotogrammetry, but also in other techniques. Lt is more simple to show the considerations for a

lD

record, rather than a

2D

record. The ccnsiderations do apply to

2D

record as well.

e. The length of the record will influence the ability to distinguish details in the spectrum. This ability is called "resolution". Wecan

distinguish two adjacent wavecomponents (and thus the details of the spectrum)

fairly well if the number of wavelengths of these components in the record differ at least one:

~~

+---

~

---L

'

----

--

--The resolution will then be about

1/

1. Evidentely, the longer the record, the better the resolution.

f. Another problem when using a digital registration 1.S the fact that

we are using values in discrete points only:

• . Af

From theoretical ccnsLderati.onsit is knovn that because of this fact

the computed spectrum deviates ver)'much from the realistic spectrum. The result of a computation Looks Li.ke

-17-The main charactcristlcs are: repetition with period

I

/

nl

and overlapping

1

around

1

2ê.l' This effect is called "aliasing". The formal proof is rather

complex and will be skipped here but an exampie may shmv why thc wavenumbers

k

and k ~

~

l

(n is an integer) will give equal values:

The values of eosine (I) and eosine (2) are identic for the discrete points

A,

B

,C, ••

•

etc., therefore the computation will give the same results for k :: 1 and k = 4:

-- "l=':>1---+1

Because of the sy~~etry of the computed spectrum the overlapping around

1/

2f1

1

occurs. To avoid confusion we must chose

I

/2Cl

l

such that the energy

of the realistic spectrum at values k greater than 1

1

21\1' is negligible.

u I

\·le can then ignore the computed energy of wavenumbers greater than

I

2111• (the wavenumber k:1/211lis called Nyquist wavenumber).

g.

If

we have obtained one measurement of seawaves and if we have obtained

the spectrum from this record, we must be aware that we have taken only one, finite record of a process which may have Iooked slightly different had we measured at another time (with the same atmospheric condi tions).

Our spectrum is only an estimate of the "truell spectrum of the process.

Getting more records and taking the average will give us a more reliable estimate of the "true" spectrum. The reliability is expr~ssed in equivalent degrees of freedom

(

ED

F

)

.

Our

aim is

to have about

3

0

E

DF

for the ultimate estimate.

k. The record of the waves is not perfect. !he values we obta-in differ

somewhat from the actuaI value s, ~~e3ha11 cons ide r th is imperfect registra

-tion as the sum of a perfect rt:!gistrationand an irregular function the

measurement deviation. Calculating tne spectrum of the imperfect registra

-tion , we in fact cal.cuLat e tlre sum of the i.ndivi.dual spectra cf the perfect

record and the dcvi3tion-function (assuming na correlation between the .

-18

-~

,(r)

1L.:

----

--

-",,,cl ",.sS.UW'It!cJ. b, "'" .:.o""'po~o:c.l ",'t S2. a...~ S ~ \lÇ;

To approach the perfect spectrum as close as possible, we must know this

devi ati.on+functi.on (:::"noise")and/or keep it as 10v7 as possib Le,

The specifications for the positions of the cameras are dependent upon the focal length of the lenses and the size of the image. ~~en using a focal length = 5

cm

and an ~mage size 5x5 cm2, the situation is:

Thc proper scale of the photographs (and thus of the spectra) can he

ohtained either from a reference length in the pictures or fron the altitude

of the came ra s or from the di.stanc e bt-!t~/eeth~n cameras. i t f irst it was

as sumed t.hat a reference length wouLd

oe

used: rn the area of JONSWAP2,

p iLe groups and ship s may provide r.his Leru.t.h , l,s it appeared to be d esirab Le to record the situation n~ar stations without pile groups or ships we are

i.nvc sti.g ating che pos s ib iLi ty of d ete rmiring t.lie distance be twe en the camer-as

at the moment of. exposure.

Wh.~nit turns out that ascalo cannot be obtai.ned i.nthis t..ay , thc spectrum

couI be «ccl.edby compar i.ngthe 20 spcc trum with a si.nnsltaueous ID spcc rrum

--_

=

Quantitative evaluation.

=

"'f\ois.e\' I---~ _

r

1

-19-from thc seasurfaee (buoy or ~ave pile).

The restrlctions on the altitude will depend upon the wave conditions. To have.an app rox imation of these restri cti.ons we can start from anticipated

wave conc.litions.These wi11 be a tunedon of wind velocity fetch and the

dur ation of the wi.nd, Esti.mates of the wave conditions may be found in handbooks. To have an idea of the spectrum near Sylt we consider station 8

during cast wi.nd, 20 knots (Beauf ort 5). The fetch is 27 km and we assume that the duration has na influence anymore.

We find: wavenumbcr. with maximal energy

=

1/

2

5

1 -1

Nyquist vavenumber > /4.9 m •

.j.o tal varianee (::.::energy/pg

=

)426 cm2•

-I m / I I 1,12~ ~.

__~

~

~

'

-+

__

'~.9~ ~-.

\ve need: a resolution to "see" the front face of the spectrum; 30 EDF; no excessi.ve"mixing" of energy (=aliasing) and a noise-wave ratio of 1:10.

Implementing this in Dur considerations we find that for station 8 the camera should be at an altitude of 330 ~ (maximum). For the other stations we find for similar conditions:

station altitude 5 230 ut 7

260

m 8 330 m 9 400 m 10 550 Ul

These figures are 0111y esdmates!

For more detailed coasiderations, the -eaJer is referrcd to App. VIII. The JONSi'-iAP 2 gr up

is

very Lnter ested in directi.cnaI meas ur-ements of

swel l . The f r cquenc y of swe lI ne ar Sylt con vary cons ider abLy (pcr i od s .

from 1.5-5 5, o r ~]avclengths f r om 340-37 lil). The amp Li tude of t.he swe l.l

can vary strongly toc. ~lich 3u~11 can be measurcd with what accuracy

I

.

\

l: -20

-During the JO~lSHAP 2 measurements a computer will display an on-line

spectrum (ID) of station 8. Froro this spectrum the specifications for the recording of the waves should be derived just prior to thc realization of

this recording. Later

in

ths experiment the specifications for the analysis will be d duced from spectra which are then computed from simultaneous

records at the se~surface (ID).

V

Camera synchronization.

Two camer as , each car ri.ed by an aircraft, shotild take pictures of the seasurfaee within a time lapse of I ms. More specific: the centres of "gravity" of the exposure diagrams should be no more than I ms apart.

• ~ <I~

This condition seems to be odd when an exposure time is used of 5 ms, say.

But the synehronization error introduces false parallax while a long exposure time intrcduces "blurringll• These two effet:ts are quite different

and the limitat'ons on the first are more stringent than on the other.

For comm::muing the camera system one could use relative time measurement

(

time

differenc,,;s between the cameras only) or absolute time measurement

(time relative to a standard time).

Using absolute time measureme.nt the commanding pulses to the cameras are

gaven independent from one anot.hcr, These independent pulses eau be

obtained in each aircraft by generating puises at a fixed interval

(4 sec, say) stDrting from a COffiIDon zero point (each aircraft carrying its

own generator). Thc~moment of ta;..:i.ng pi.ctur es can he chosen during the

flight for Lnst.mce by transEer ri.ng the gcnerated pulse s to the camar as:

by a sE:?erate cOffiJlElnd(for i( st:1'1-::einitiation and termination of a sequenc e Dy vo ica couaaand via radio):

-21

-Ta geue rate two pulses Lndepcnd cutLy during a flight of two hours, say, which

should be less than I ms apart, demands high qualifications of the time

measurement equipment. A mechani sm is needed which may show only a relative error of 1.5xIO-7• This equipment does exist (for instance crystal-08cilators).

Using relative time we transmit a pulse to the two cameras which then

expose the film. Beeause such a transmitter was available (either the board radio of the aircraft or the transmitter of one of the camera types)

this methad has been ehosen.

It was found that between the eommand to the photographic system and the starting point of the exposure a series of delays occurs.

\

_j_

Only the light entrances to the cameras are tobe synchronized. The other

pulses of the system may occur at any time.

__~

__

~

~__

__

1

_\

l:."o."!.\Mt":>iOvl

5

C"""",zv-o.. ~

_

-,-

1

_

_

/

L

The time delay between the pulse to the camera and the film exposure

con si sts of two parts: 1. electron i.cdelays

2. mechanical dclays

TIl(! secend ene rs by far the most important whil,ethe f irst ene l.S negli+

gible.

The cameras avo.ilable for the experiment were:

a. Speci.J.l aer ia I survey c ainera s (ov]11,;;dby comme r c i.a I fi.rms ) ,

av o, \-lildRe 8 and Re 5

-22-b, Le ss sophisticated came ras (owned by Ri jks« ter staat ) •

Hasselblad 500 EL

A very inportant qualification, a art from synchronization. is the geometrie

performance of the cameras such as lens distort'ons, mechanical toleranees et .

Ihe aer i al survey earneras are very attractive in this respect and it was tried to synchronizc the

R

e

5'5

.

During tests on those ea~eras it was found though that t.hetotaI time deLay amounted to 500 ms. This wo u ld

not be too bad if this time Lapse woul.dvbe constant for each exposure.

But the standard deviation appeared to be of order of 10% or 50 ms!

To reduce this variabiLity would have required a major alteration of.the

camera construction. Ihis was considered to be impractical.

The other types of aerial survey eameras have a variability which is even

grcater (up to }-2 s). Ihis is 'caused by a special construction of the

shutter blades (rotating blades). The moment of exposure is then chosen at

random (within one or two seconds af ter the command). This construction

may be adapted for instanc~~ontrolling the speed of the rotating blades

but the results of one such attempt were rather disappointing (Technische

Hochschule Aachen): tne synchronization error was decreased to approximately

40 ms with a considerable deviation (order of 40 ms). Apart from the syn

-chronization problem these cameras have another dra-hack: they are oHned

by commercial firms•.This would make the t..hole system and the use thereof

dependent on such a firm.

T~1eHasseIblad cameras do not have the qualifications needed for proper

photogrammetric.evaluations. These cameras have apparent geometrie

disadvantages:

The film is not sufficiently flat during exposures (the aerial

survey c<Jmcras have a vaCllum device to flatten the film).

The lens gives unknovn dis t.ortions of the image.

The construction of thc camera exhibits unacc(!ptable tolerances.

It appe~red thought that syuchtonization could be achieved relatively simply.

Instead of synchroni~ing the aerLaL survey c~~eras, to be achieved on1y·

by great effort, it could be tricd to iw~rove on thc geometrie charac

-teristics of the H~ss~lblad cameras. It was decided Lu Jo the latter.

1h:.:> dcc is ion ha s a l so been Lnf Lue nc ed by t.he fac t r ha t these c ame r a s , a tran.smi.tter and :;c".l0rarecel ivers we r e constantLy availabl.c.

-·2J-Up till nov the geometry of the came ras has been ad apted

A vacuum film fbtt'ning device has been built in the cameras.

'I'oleranc e s of film-cassette movements are decre as ed by a plug -construction.

The distortions in the image wilI be calibrated by standard pictures.

During tests in the laboc:ltCJry

c

n

the mechanical delay

in

these cameras, it \oI'a5 found that this delay is rather short (order of 30 ms ), while the standard deviation was very sroall (order 0.5 ros). lly incroducing a deliberate and adjust.abLe eIe ctrorri,cdelay in the command+cha i.n, the

total of electronic and mechanical del"y ean be chosen (for instanee 40 ros):

~1_C::=J

--,--

5

L~C::::J--_L___

_____L_

J

'

~-t:.1"'-n..."',tt"", p",\!.e ~.:>

c.o..Vit\.e:.'1"0.

J

\

----~----

--

--

----

---

--

~

--

--

--

--

-tV"'o..YI~Y\O\\..L!,)~OV\ o..d.)lA.~'to.\c.\e

ó..,lo,'3 elec\::V'",'OI;c.d.el",':)

~"'-\Ow "" a.\.}&.",o.~Q!

""".0"'0.";00..\ cl.ela'j

It is assumed that the average value aud therefore also the variatiou of the transroission delay is negligible. So the total delay in both a irpLane s have a known average value while the deviations can be small. During tests in one airplanc (cameras eonnect~d electronically, without radiolink) the delay was set at 35 ros and the synchronization error waD found to be 0.04 roswith standard deviatlon.O.3 ms (App. X). In the

ultimate system we plan to have a di.splay of the response time (electronic

and niec.han ica I deLay) for each picture. vle ;'Ji11 then be able to eliminate non-synchrünized pictures by selection afterwards.

heLi.copter s se crns to be most adv ant aguous , l'i::es(!-airpLane s , the crews

VI Ai rp l anes,

To obtain the po~itj.on o[ the cameras (thc platforms) oue could think of tove r s , b li.mps, air pLane s and he li c opt•ers, In thc framewo rd of JONS~IAP 2

rnd pos sibLy other s rudi.«, in Holland the pplication af a irpLane s an

aud UI>': faci Li ti.es ,-lil have to meet, norce s.t<ln',~.l:rds to bc qua li f i.ed to c ar r / out eh", procedur e,

-24

-I. EacilitLes to carry a camera, which will be photographi.ngvertic lly.

The consequence is that eithe-c a "hole" in the floor Ol:' a construction

outside the eabin should be available.

2. The control of aircr3ft navi~ation should be such that the deviations

are acceptable: - vertieal angle Jeviation of camera axes 30 relative,

SO

absolute.

- altitude deviations 10% relative.

'I'he crev should be abLe to control the mutual position of the airpLanes

(distance

=

(

40

%

+ 10i,) of altitude).

3

.

Flights over ses at relative low altitudes (relative to normal aerial

survey flights). In this case one hundred to several hundreds of meters.

4.

The aüplanes should be available at a stand-by basis during the month

of September 1973 (preferably near or at Sylt).

Based on thc assumptions of chapter

I

V

the airplanes should take

positions at the stations near Sylt according to:

station max. altitude corresponding rnutualdistance (=

0,4

altitude)~

5

230

m

9

0

m

7

26

0

105

8

3

30

13

0

9 'tOO 160

10

5

5

0

2

20

If single engined airplanes are used during the ope

_,

rations, the crew wants

to have sufficient tbue to le've ths airplane incase of motorfailure. A

minimal altitude of several hundreds of meters should do, but this excludes

a great part of the stations. Helicopters eau be used down to lower levels

but at approximatcly 75 m the dowuwash of the blade s is di.storti.ngthe

seasurface (depending on thc velocity of the helicopter).

The negotiations to obtain suitable :ircraft have been g01ng on for

quite somc time ~-lith rniILta ry authoritie s and commercial f irrnsin Holland

-2

5-VII Coucl.o si.on,

It has been found thnt it is desirabie to obtain au interpretation of

t.he spatial struc ture of seavaves in the framevo rk of an international

seawave research pLoject, r~11ed JONSWAP 2. This project is ~imed at testing

theoretical COnCè?ts of wave generation and attenuation. The measurements

ca be used in .he framewo rk of this project but a1so for applications in

ot ..er fields (mari.na engng,, coastal engng. etc.). The technique for recording

th€.wave s will be auad aptati.onof existing stereophotographic procedures,

It may be used for future ~_nvestigations of wavephenomena,

BJ.sed on considerations of the anticipated wave conditions nnd .

practical experie~cet specifications for equipment and procedures have

been obtained. The organization, finances and material support have been

agreed upon by Ri.jk swater staat and the DeLft Unive r sity of Tcchnology.

The experiment was initiated in January 1972; in September the experiment

vas incorporated in JONS~IAP 2. The development of the equLpnient and the numerical analysis procedures has started. The realization of .JONSWAP2

is planned for September 1973, the publication of results in 1974 and

1975

.

-26

-IX RI.:FERE:CES.

1. Bar nett , LP. et aL, H:·ieusuren:ents of wind-wave grovrh and sve Ll decay

during the Joint Ncr t.h Sca ~a'J'e Project (JO.lSt\'AP)".

To be published in the Dcutsch e s Hydrographisches Zei.c schrift, 197.1

(possibly Hasselmaln, K. et al.).

2. ,ergland, G.O., "A gu i.d.cd tour. of the FFT", IEEE Spectrum, July 1969,

pp, 41-52.

3. THackman, R.B., 'I'ukey, J.H., "The mea urement of pow r spectra", Dover

Pu Li ca ticns Inc , , New York , 1958.

4•. Coo Lay, J.W., Tukey, J,W., "An algor itm for the machine calculation of

compl.ex fourierseries", .1~\th. of Computati ons , vol. 19, PP. 297-301,

April 1965.

5. Cote, L.J. ct alo, "Tne direc ti ona I spectrum of a ....ri.nd gencrated sea as

detezrai ned from data obta i ned by the Stereo Wave Observation Project",

Metcorological Papers, vol. 2, no. 6, June 1960, NewYork Univcrsity,

College of Engineering.

6. C'ru se c, J. "Pho togrammetr ic measurement of the sea sv= Ll.", Pbo t.og'rammetr i.a, .

IX, 1952-1953, pp, 122-t~5.

7. llasselmann, K., "On the non--Line ar ener.gy transfer in a gr avity-wave spectrum.

I: General theory", J.Fl. Hech., 12 pp 481-500, 1962.

8. HasseImann, K., Sehieler, .M., "Radar backscatter from the seasurface",

Eighth Symposium, Naval Hydrodynamics, ARC-179, Office of Naval Research,

Dep. of the Navy, 1970, pp. 36J-388.

9.

Holthuijsen,

L.H.,

"E

n

i

g

e

optische methode voor het meten van zeer

kleine watergolven" Technische Hogeschool Delft, Afdeling der Heg- en

HaterbouHkunde, vakg r ocp Vloeistofrnechanica,· report R1971/11/D, 1971.

JO. Hova rd , C.D.D., "Pho togr ammetr i c measur ement of direc ti onal wave spectra" t

Winnipeg, Manitoba, Canada, De amber 1969.

11. Kasev i ch, R.S., T,l,g, C.E" lIE,~I...::rSY spectra 02 seawave s f romphotogr aphi.c

Ln cer pr ctat ion "Seven th Symposium on Remot;e Scnsi.ng of Environment, Urri.ver+

sity of Michigan, H<ly 1971.

12. Kryl.ov , Y.1:>f" (cdüot:), "~'7ind \~;1',es"J Collo (S;~)., Lno strannaya Li ter atur a, 1962.

13. Longuct-HiG;~en5, H.S.~ Cal"ti-n:ir,ht, D.Z., S~.~:ith,~LD., "Obsc rva tion of the

d i.r ec tiona I s pectru;n of 52C:'.,;;i'J·~Sus i.ug th e ucticns of a f Loati ng buoy'";

24. Snyder, R.L., Cox, C.S., "A field study of the wind generat:i.on of ocean waves", J. ofMarineres., 24,141,1966.

I ,

-27-14. Matushevskii, G.V., Strekalov, S.S., "Raschet dvukhernogo energeticheskogo

spektra po dannym stereofotos" (Calculation of the two-dimensioual energy

spectrum from stêreophotographs of waves"), Okeanologiya vo1. 3, no.5, 1963. ;

15. Ministère de la défence nationale, Secrétariat d'Etat

à

la tlarine, Comité

Centrale d 'Oceanographie et d 'Etude des Cates, "Restitution photogrammetrique !

de la surface de la mer a I' aide de vues aeriennes syncbroná se es",.'Bulletin ,

d'Information, IVe Anriée, no, 10 December 1952. I

16. Nota Rijkswaterstaat, "Nota Golfmetingen met behulp van fotogralllll1etrie",

(1962, estimated date). I

,

17. Pierson, W.J. Moskowitz, L., "~ pr oposed spectral form for fully developed

wind seas based on the simÏlari ty theory of S. A. Kitaigoradskii", J. Geoph.

Res., 69 pp. 5181-5190, 1964.

,

18. Panicker, N.N., "Determinátion of directional spectra of oc.e.an waves from

gage arrays", Berkeley, University of California, Hydraulic. Engineering

Laboratory, Techn. Rep. HELI-18, Aug. 1971.

19. Schule, J.J., Simpson, L.S., Deleonibus, P.S., "A study of .fetch limited

wave spectra with an airborne laser", J.Geoph.Res., 76~ no, J8, pp.

4 I60-4171, 1971. ~

20. Schumacher, A., "Stereophotogrammetrische We11enaufnahmen11·'" -wisseErgeb.

Deutschen Atlantischen Expedition auf dem Forschungs und Ve.om

essungs-.schi f f "Meteor" 1925-1927, Oceanographische Sonderuntersuchungen, Erste

Lieferung, Berlin 1939.

, , f

21. Simpson, L. S., "Pre l iminary investigation of the directiona1 spectrum of \

ocean wave height as obtained from stereo wave photogr apha'"

1

Informal manuscript,

u.s.

Naval Oceanographic Office, Wasbington D.C., ~

Jan. 1967. '

\e

22. Sing~ton, R.C., "An algoritm for computing the mixed radix: fast fourier

transform", IEEE Transactions on Audio and Electroacoustics.., vol.AU-17,

no. 2, June 1969.

23. Sloane, E.A., "Comparison of linearly and quàdratically modified spectral

extimates of Gaussian s ignal s" , IEEE Transactions on Audio and

Electro-acoustics, vol.AU-17~ no, 2, June 1969.

25. U.S. Naval Hydrographic Office Pub. no , 603, "Practical methods for

observing and forecasting ocean waves by means of wave spec~a and

statistics", 1955.

26. Weleh, P.C. "Theuse of FFTfor the estimation of power spectra: a method

based on tim.e averaging on short, modified periodograms", IEEETransactions

App. I

List of (potential) participants of JONSWAP 2.

Canada Denmark England France Germany Holland U. S. A.

Bedf

ort

I

n

st

i

t

ute.

Un

i

v

ersity o

f

British

C

o

lum

bia.

Atomi

e

E

n

ergy

Co

mm

issi

on

.

Nati

o

na

l I

nstit

ute of

Ocean

o

g

raphy.

Unive

rsity o

f Sou

t

hampton

.

Insti

tut d

e Mech

.·Stas

t

i

s

t. d.I. Turbul.

U

ni

v

e

rsit

ä

t

Hamb

urg (coo

rd

i

na

tion JO

N

SWAP 2).

J

o

han

nes Gu

tenber

g Uni

ve

r

s

ität.

I

ns

titut für

Ra

diometeo

r

o

l

ogie und

M

aritime

M

eteorologie

.

D

e

u

ts

ches HydrograRhische

s

Institut (coordin

at

ion JONSWAP 2).

5 ••

F

o

r

chungsanstalt der B

u

nd

e

swehr f

u

r W

a

ssersch

a

ll und Geop

h

ysik.

Ko

n

inklijk Nederlands

M

et

e

orologisch Instituut

.

Rij

k

swaterst

~

at

.

Technische

H

ogeschool Delft

.

Oregon State University

.

University of California.

University of Washington.

R

a

ytheon Company.

University of Miami.

Research L

a

boratories

N

OAA, U.S. Department of Commerce.

University of Florida.

Nova University.

NR

L, D

e

pa

rtme

nt of the Navy. ,

Nas

a, Langley Research.

App. 11

Sci

e

ntific obj

e

c

t

ives o

f J

O

N

S

W

AP

2

(t

ak

en fo

rm

a résu

m

é o

f

a JO

N

SWAP 2

m

eeting).

Th

e f

irst Joi

nt N

orth S

ea Wa

v

e

Proj

ec

t (JONS

WAP

1) in July/

Augu

st 1969

yielded a ra

ther

convi

n

ci

ng

pictu

re

of the ov

era

ll energy b

a

lance o

f f

etch-li

mi

ted w

a

ve

spe

ctra.

In

p

ar

ticul

a

r

it w

as pos

s

i

bl

e to ex

plain

the s

hap

e

a

nd

evolutio

n

of the wa

v

e

spe

ctr

um a

s

a

sel

f

-

s

t

abi

lisin

g p

ro

p

erty of the

n

onl

inear

energy

trans

fo

r.

Ho

w

e

v

er

,

a n

u

m

ber o

f q

uestion

s remai

ned unresolved.

~

Th

e

most i

mp

o

rta

nt of t

hese was

t

he mec

hani

sm

o

f

energy

transfe

r fro

m

the

a

t

m

o

sp

here to

the

wave

f

i

e

l

d

. Ot

her

q

ue

stions c

on

cerned th

e c

oupling

be

tween

v

e

ry short

an

d l

on

ger

waves

, the

mec

h

a

nism of en

e

r

g

y diss

ipat

ion at short

w

av

e

-lengths,

the

detail

s

o

f

the

ene

r

g

y bala

n

c

e

o

f

a full

y

d

e

veloped spectrum,

the role of

gus

tiness for the spectr

a

l evolut

i

on, and the si

g

nificanee of

scattering bY

'

bottom i

rreg

ulariti

e

s for the obs

e

rved att

e

nu

at

ion of swell

in

s

hallow

wat

er. It was

re

cognised that a seco

n

d large-s

ca

le wave p

r

oject

would be nee

d

ed to investi

g

ate these questions.

Following a nu

mb

er of informal discussions with individual groups, a meeting

was held in

Ham

burg form S

e

ptember 12th through 15th, 1972, in which all

prospective participants attempted to define the objectives and clarify the

logistics of JO

N

SWAP 2.

The above m

e

n

t

io

n

ed questions were accepted as defining the ~

of

JO

N

SWAP 2. In addition, the follo

w

ing auxilia

r

y objectives were agreed

upon as natu

ra

l and co

nvenia

n

t

e

x

t

ensi

o

n

s of the core p

r

o

g

r

am

:

I)

The rel

a

t

i

o

n

ship b

etwe

en radar-b

a

c

k

scatte

r

signals and the short

wave-len

gt

h range of

t

he spectrum (including inter-actions between

'

short w

aves

and long

w

aves).

2)

Invesit

g

ations of the

E

ckmann (planetary) boundary layer.

3)

Measure

me

nts of he

a

t

fl

ux by co

rre

lation

an

d infrared

t

echniques;

correl

ati

on of th

e

v

aria

bility o

f

heat

flux w

ith th

e

v

a

ri

a

bility in

(~.:-~..::Jl~:!."'i':':1, L=;·~:l~!"~'.;:t..:i:J.n) _{Apr. III} ~~::·t:.l...'i·~;·",!'":-:.:~

-

----

-

-

-

--v.H. S:_0;::d::"n 0!:::,vèrsity of :?loriè.~ Gai:'_esrI·L'Le, USA ;~e5ac~e flu~tuBtions CL) at a single

~Jr::"~. positicn fol1owing the water

eur:ace

dow~3trea~ a~d vertical wind velocitr

fl~ctuatic~9 (3) at a single hor1zon~. Do~itic~ an~ at varioue fixad elévat.

~bove =ean surfacd

su.rfaeeelevation at single hori:r:.posit.

pressu~e tluctuations (E) at 4

~or~~. ncsitions and at varioue

iixad eievatior.s above taean surface

f;·:~:'?ce elevation at several hoz-Lz, pJsitiol1s !:.eanwind ~~,~edat a single posit. and fixeii e Le vatLon r''':j ~ .~ _'~Ij;,. t,,~._,.:"( station 8

underwater support near PISA (3-post conatruct10n +

in-strument stage 10x15m on w.f. !è1!>~: probabl: "OT2" or

similar (35 m.long) 1 small baat (outboard) motor) tor inspection additional: 2 ëmall boats during installation 4 persons on "OT2n

2 divërs on "Gauss"

16 chennel own data acquis-system on ship

additional: PCH telen:etry system ot "Pisa"

intercomparison meaeure~ents of pressure sensors prior to experiment

?'W. Do~son

J•.A. Bll::'ott 3edfo:-jInst1t•. Dart~outh, Canada

p::-ess""'feluetuations (L) at a single

horiz. ?osit10n tollowing the water

surfs.ee

press~re !luctuation (E) at a single

~~r~~. p08i~::'onend fixed elevetio~

~i~d velocity fluotuatioDs (1) at a

sinsle hori~. positio!lfollowing

wate!' 8ur!ace

....:."';1 \'sloeity_profiles at single

~cri~. ?ce1tion ani,varioue fixed elevat:'onsabove :nee:;.s',lrface

rinj vsloeity fluetuat10ns (E)at a

single hori~. posit. and fixod

elevatio~

S~;:,f2.eeelevation at e. single hori!:.

.?osition

l

ei

"

~e:J:psl'tura!)fluctup-tions (E)

·,-:!....-:i:tity f'u~tu?:tiQnB R.L. Snyder Nova Univeraity Ft. LauderdalA L. Long Univ. of Miami Hiami, USA etation 5

~ubmerged tripod and small

mast within 1.2 m of tripod ~: "Wegan (30 m long)

1 rubberieed canvas, outboard powered

2 divers on "Wega" 3 person3,on "Wega"

\.

•

•

analog tape rec.orderon ehip, want to use the German cocputer facilitiea (probably Hannover) ovn aoft;.-are

intercomparieon of pree3ure sensors prior to experiment

--e "P ~

-!. .',_

'

--

..,

pressure seneor on Wave follower

(servosystem, ca 3,5 m stroke,

on top of underwater support)

probably x-wire anemometer on

spar naar wave follower

gravity and capillary wave spectra,

wave follower + capillary wave probe

on top of w.!.

pressure eensors on instr~ent stageon top or underwater 6~pport, remotely controlled ~ght of instruments d:i.rectionalwave 8p~,pressure wave gages Q.IDl anemometerS ~ressure sensor on wave follower (hydraulic ocrvo system, ca. 1 m

stroke, on top of submerged tripod) •pressure sensor on small Itast

~

Disa hot-film anemotleter close to

presaure aensor on we7e follower

8a~e as above on wave follower, mean

(til!:.eaveragedand wave pha

se-avereged) velocity profilea instrument ~ight variable by w.!.

Kaijo-Denki sonic anemometer at

fixed emall mast

ona dim.gravity and capillary~

~eetra, wave follower+ wave sensor

on wave follo~/er(resistanoe probe)

temperature sensor ,1y!l1ando-meter

L. i~.s...1~)e !-:. Dur~c }:al E. Au;;;etein D. Sch:-iever ~i~d vel~city fl~ctuations (E) at 2 ~o:-iz.?o3it. ~,d~ixed elevat10ns atove ~een surface ~i~d v locity_profile~ at 2 hor1z. and

5 ve~t cal posit~on3 abcve ~ean surface

w:~ict rectic= in 2 vertical p031tions =ds~ec ively 1 vertical position

~i~ te~perature fluctuations (E) at 2

~cri~. ~ositions and 5 vertieal roeitions ebove mean surface

;';"!!üdó ty fluctuations (E) at 2 horäz, p~81~ions a~d 2 respectively 1 vertical

~o9:'t:'on

'",~'t('r te:-:'0er3tur(Ee) at 2 fixed hori:!::.

cná at; 5 de'p~

vertieal wind profile measuraments up

-:;0 1.k!!l lligl1t

'.Tertical-C1'o1'11eof ter.:lperaturande

i:;.:.::::'dity_ {density) up to 2-3 km hight p09sibly; 2;.3. 5t:.9Ch Dan tsh A.ECRISÖ Roskilde,Den.:::ark wind fluctuat10ns (E) at 1 horiz. p:sition and 2-3 fixed vertical pcsitio:ls a';)ove!:lear..surface

Metcorol. lnstltut

of the University

of Hal!lburg

R~burg / Germany

x-wire and sonic anemometers on one

meteorolog1cal needle near ~P1sa~

and one oeteorolog. buoy (I)

~p anemometers jon one meteor.needlèI

and on one iree

wind-vane floating met. buoyII

and on meteorolibuoyI

~perature sensors at same needle I

and buoy II

1yman~-and micro-wave-refractometer. at meteorol. buoy I temnerature sensors at IllstoO:::·ol. needle Cl) and at meteorol. buoy (II) pilot balloons: meaeurement of dist. and d1rection irom ~Planetllwith radar radiosondes every 4 hours

x-wire anemometer on meteorol.

naedle (II)

station 8

big mast IIPisall

.2 meterologioal needlea

(masts)

shi:p~ IIPlanet"(80m long)

+ unetabil. meteorol. buoyIr

probably "Alkor"(30m long)

+ stabil. meteor. buoY+J

several rubberized canvasee

14 persons on ":?lanetll

8 -10 persona on "Alkor"

station 8

meteorol. needle (II)·

i PCI{-telemetry syatem for "Pisa"

i and 2 meteorol. needlesj incl. 2

,2 PDP 8 computers

I own, analog tape recorders

! and data acquiaition aystema

i on ahä pa ,

,own computer CDC 1700 and Terminal

I for Hannover computer CDC Cyber 76

!

I

storottwaralle tor tiparticipame snteeries analyais

PCM-telemetry system of "Piaa"

participation needa con!irmation by

.A.ECRISÖ

C.Oost

::

.

]3

CU'w2

Ko.::.in...1(:'i jk Nederlands

l-~eteorologisch

1!',9t1tuut

De.3ilt, ~eth6rlands

wi.::.dvelo~ity fluctuntion3 (E)

&t a si'::'ölheoriz. position and

2 fixed vertical elevations above zee.::. surface and at sacond hori~.

position and 1 !i~ed vertica1 e1e

-vs.t:.o:J.

surfaca alevation at 3 horiz. pos.

"Trifahnanll on meteorol.

needIe (II)

probably one Tri~ahne on meteor.Tripod

near Hoernum pila

one dim. gravity wave spectra

3 Waverider" buoya

S'J;ation8(5)

sl,il2..·;

"Gauss-2 pereons on "Gausell

additional 1-2 persons

during instal1ation

at 3 different stations (a.map)

PCM-telemetry syatem ot "Piaa"

data processing: own and

Hannqver computer

own telemetry aystem tor "Wave

ridera-and recording ayatem

compariao~ teate ot 'Waverider witll'

station: 10 km normal to

station 8 (north) a.map

...r•';',~ :''; 1~.,.:

_4__. . . --- ..----.--- "* '_'. __ ._,_•.•••• __ .._ __•__-.. '.._ "_,'.40.

.ea.m;estati.on.

O'lio'It s!:.i.p_;"'Murray·

_ :;. pe:rsOllS on. ship

surfacecu!"rents a:ad orbitalvelcci.

-ties,electro~gnetie cu=rent~eters

direct. grav±ty wave spectra

additionsJ. uae o:t=Pger cU-au,a:+ !:!l1p.!!:lrGatulS'(2 persolU3}at_ ot.S

photog;:g.PM by iJldivi.dtoal. g;..·oupson QKoerte'~(2persollS) at st.5

ah1ps

~

---

--

---

--

--

---Nr,t.1on, .~n!Jt, of O('t;,a:1ot:rnp~:y \0'0r:::1.tl7, E!:glar.d .!U;-:Flç:_Lel.QY~ at a single po s ;t:'C;1 ~~~e~ts in sur~~ce laye~ et 3 lav~ls ~~d 2 hori~. posit1ons ..•. Wslè,;n R. Carlson K. :2.ichter

s·.u-.faceeJ.eva"tion at several positions

~ean s~~?ce alevation at 2 poeitions

c~~rente in aurfacelaver at ~o levels

SJ.da~51e horiz. positron

L.H.:!olthuijeen

Tec!"-":',ëscHohegesc!lool

Delft / Holland

surface elovation of a cartain area

Vil feteh

R..T. roll~t"d

U:liver:Jity ot S,)Uthampton

Southampton / England

directional gravity wave spectra,

pièCh &raIl bucy

electromagnetic-and vectoT

averaging

fYACR

)

current maters on spa.r buoy a.~d.m.ocn:ing

Deu~sche5Hydrographi

-schee Institut

Hamburg" Germany

directional gravity wave spectra 2 pitch &: reIl buoys ene d1~~y w~ve s~~.at"

4

horiz. positions d:1.rectior:.alp::revity(8;(01)) wav~ ::.p~ct:ra

pre8s~re gage (iO} array at Z horiz.

positLone (fer wave'-botto!llscattering

measurementa of swe11 diss1pation

2 tide g~g~

·twodim. grav1ty wave spillm

by-stereophotography

own data recording end proces6ing

probablyown computer on ship

~~:u..:~~-.::;e:.::n~dt..,',..:8::;(n'.<lraens '",."'Gauss'"

J

"Piss" • WO nee<D..es)

"':a:oe:r:IlUllt"pile,. me.tearol.. tr1.pocl)

etat:ion 8 and.5

·Pi..sa" PCKtelemetry .B7atelll

probab13' wHoernum."PCK tel.sll:etr;r ~ ovn telemetry syetem

0'i1n data. :recor~g Wld

eequis1.t~on s:rste:

l.og:Lat1.ccoorclinati.on o~ Jcms-1(J.P 2

etation: 6 and 5 (P1.sa..K:)enllm p.)

statio;&. B (l"i.aa)

Olo"l1Jdata.processing

H' poscs1b1e 5 nights dllr'illgeast-vi.nd 6 speetra each ~11ght

~~ poselb1c 2 spectra in 1-2 sec d1sta

:1.n order to ex.cl.ud~SJltb1gni.ty o~ e~re apeetr' di.:t=!erent ~1gbt routea

2 a1,rcra!h: (2' Duteh.'Cesaua.'.,

or 2 he1.1eopters) airport: Westerla!1d

6-8 paraoJW at a.irport

A. Rerwig

P. viills _BundPors-Ch_eaungeana_wehrttirtalt_Waazeder_r -echall ~d Geophy6~ Kiel, Germany

su:-f<lce elsvetio:1 at a single

pcsi"ion ~~d v.s. fetch _wavone _edi_sm_p._ectg_rr_aa'rtt

_o::r

y₁and_aBsr-c_?a_ro!p111~-y_ilolllete__r

on "Pisa~ and 8al!I"'~' ~,

helicopter

stat1ón 8

."P:1.sa." s.!I.d di:!:!. ni.~t routes

2 per-ecnaon -GaUlJ3"Or"P:l.anet'"

nirport: Wosterland.

ovn ans..logtape recorder acl

PCMtelea:et-:;r"-ll7atea o:!

,.ta'.!.,..J. '....11.·~~'.;:,.!. û..t.rÀo'Ul.~t.:L Wûow\:. ...:a:-l._••.l. ...

.

... .'- ". "~ .

-

---

-

_

.

_

__

.

_

-

--

---

-

I , ! A',. _, _\t..~....V:_",;'G _! c.:.y'..~:.:>::-.:~(;GL-:?~.r.y ~\.._:.y.1. ~'"-:~ , U~;,\ ?~O·C07~~~tYof ~rs ·?UrfaC6 at 2 dám, cap;,ll;-rry~~1U'ect:::'9. by eta.tion

a

photorecord~g 0= ~11m

a. ~::":...;le :ç~aitäor; QPtical Fourier ~"<,,!1.stJv-:·!!:t9cl:~iqua;- "1'1&&'" data proceas~ et Johna Hopkina

obliqua looking c~~ra on be~ of Pisa _{2. persons on "Ga.uss"}

:~yJ.i~~t :trr.:~d-:ar:::.e pr.oto"'eter(teleecop) on.bcaa c:!?isa . ,,1) ,srcooperat:!.onvi.th ~~ra..-..edD:.ea.surellten.ts operat1oll:ot 1:nstr.z:menteOll _1.ea '(86e C.B. Katsarea

pc s cioLy :

D. ::~il·.r..~ll. jr.

:D~:;e.~t~ent cf tha "!Zavy

HE!.

~~2~ington D.C. / USA

:;Jl:!O"C;Ct;~2Y or sea-S1J.rfECeat ~ dim. grav1;;y3.ndcapillli\ry~ difie-ren-t!J.ightlla-tte-rns wants to partic1pate.

one posi,,;iO!1a.nd V.8..1~~tch §pectra by optical POUrier transform atte~pte to provide camerae, techniaue one aet of oamerae in, wiJ.lthan uaa D.B.Roas aircraft

aireraf:!;

.

one oblique looking camera on ~ne (station 8 ?)

mast { Pisa ?}

D.B.

Ross U.S. :Jepa::.'tment of comnerca rO_t_~ ~i(;'::li / USA.

s1;;:;:-fëCil eLevatacn va. fetch ene dim. and directionel '\'lavesEectra different flight patterns own recording and data

as function of foteh. airborne Laser acquisition

Profilometer _{own data process1ng}

white cap density~vs. fetch photograph1c camera ,aircraft: DC or C 130 or

other D.B. ROBS is coord1nating the

ab?ut 10 persona e_ctfo_{rafts a}rte to pro_{nd thair uae}vide two U_by S_theair -po e aLbLy r

f

american groups

(see: D.H.Lanachow, S. Parkar,

S. Ea::-ker J. Wr1ght, D.Stilwell. M.Miyake)

NASA Langley aesearch

Center

Har.pton

I

USA

radar b~ckacatter men6ure~ent8 ~p111ary wave á'Oeotra,nQn

ySQ

aircraft or other no answer to invitat10n (arter JONSWAJ

.fH.:. !:.U;P';C!l!Tl f lrp..dlo;n,~~e;r see D.B. Roaa) meeting) untiJ.now

poesibly: J. Wrig~t

D~~~rtmcnt of the Na\~

~!\L

il'lishington

D

.e./

USA

radar ~ack2~attor ~easurementB capt._llarywave spectra eircraft (eee D.B. Ross) or no answer to invitation.(after JONSWAl 4-frequency redar system 8ta~iQn 8on "Pisa" meet1n~) until now

t:a3sibly:

D.H. Lonscho...

riCA ..H.

Bç\~lè(H' / USA

~_\.;:~~~ t"".t.:J

~;.r.:~

_...

~1!1.~L!r:.'!~.ro::onta g~probe eyatem cocbined with De Haviland Euffalo. ah'craft no answer to invitation (~ter JONSWÁ,!

_____ .,,_ 4___ 1nert~Blnuv1gat10n aystem meeting untiJ.now