D.A. RICE U.S. Coast and Geodetic Survey

Secr~taire de Is Section IV

COMPTE RENDU DES REUNIONS

DE LA SECTION IV- GRAVIMI~TRIE

Eigh t m e e t i n g s w e r e he ld to r e c e i v e r e p o r t s and d i s c u s s the n o r - m a l Sec t ion a c t i v i t i e s . In addi t ion , the Sec t ion p a r t i c i p a t e d in a joint s y m p o s i u m with Sec t ions I, IH, and V on geode t i c u s e s of a r t i f i c i a l s a t e l l i t e s , and a l so he ld a" joint m e e t i n g with Sec t ion V to a s s e s s the po t en t i a l con t r ibu t ion of new g r a v i t y m e a s u r e m e n t t e chn iques t o w a r d the so lu t ion of geoid p r o b l e m s .

.Reports were presented by six Special Study Groups on develop- ments of the past three years; m~ny of the questions had been discussed in s o m e d e t a i l a t the t r i e - - ~ l m e e t i n g of the I n t e r n a t i o n a l G r a v i m e t r i c C o m m i s s i o n he ld at P a r i s in S e p t e m b e r , 1959 and in s p e c i a l m e e t i n g s a r r a n g e d a t He l s ink i . The Spec i a l Study Groups a s s o c i a t e d with Sec t ion IV are :

S.S.G. N ~ 5 - World 1st order network-connections between absolute gravity stations - selection of a unique reference sys- tem (Chairman : Prof. C. MORELLI)

S . S . G . N ~ 5a - T e c h n i q u e of g r a v i t y m e t e r o b s e r v a t i o n s c a r r i e d out on land (Cha i rman : Dr. P. HERRINCK)

S.S.G. N ~ 6 - C a l i b r a t i o n b a s e s E u r o p e (Prof . M. KNEISSL) Nor th A m e r i c a (Mr. D .A. RICE) C e n t r a l A s i a (Prof . Y .D . BOULANGER) E a s t e r n A s i a (Dr. T. OKUDA)

S . S . G . N ~ 17 R e s u l t s d e r i v e d f r o m o b s e r v a t i o n s on a r t i f i c i a l s a t e l l i - t e s as r e l a t e d to the e a r t h ' s g r a v i t a t i o n a l f ie ld ( C h a i r - man : Dr. A . H . COOK)

S . S . G . N ~ 18 - Methods of abso lu te g r a v i t y d e t e r m i n a t i o n ( C h a i r m a n : Dr. A . H . COOK)

S.S.G~ N ~ 20 - G r a v i t y m e a s u r e m e n t s at s e a , e i t h e r on s u b m a r i n e s o r s u r f a c e sh ips ( C h a i r m a n : P ro f . J . L . WORZEL)

M a t t e r s of p a r t i c u l a r i n t e r e s t d i s c u s s e d a t the v a r i o u s m e e t i n g s a r e s u m m a r i z e d below.

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FroST SESSION (27 July)

FoLlowing an i n t r o d u c t o r y a d d r e s s by the P r e s i d e n t , the Sec t ion r e c e i v e d a r e p o r t by Dr. S. CORON on the a c t i v i t i e s of the I n t e r n a - t i o n a l G r a v i m s t r i c B u r e a u for the pas t t h r e e y e a r s , a p e r i o d m a r k e d by the u n t i m e l y p a s s i n g of F a t h e r LEJA Y and the a s s u m p t i o n by P ro f . TARDI of the du t ies of D i r e c t o r of the B u r e a u . More su i t ab le office q u a r t e r s in P a r i s have been obtaIned for the s taf f of 4 o r 5 people , s o m e of whom a r e employed p a r t - t i m e . The o f f i c e i s ope ra t ed u n d e r the d i r e c t i o n of D r . CORON. An i m p o r t a n t add i t ion to the r e g u l a r B u r e a u a c t i v i t i e s is the p u b l i c a t i o n , twice y e a r l y , of a B u l l e t i n of I n f o r m a t i o n con ta iu tng an u p - t o - d a t e r e v i e w of w o r l d - w i d e g r a v i t y a c t i - v i t i e s . D r . CORON a l so s u m m a r i z e d h e r r e c e n t l y pub l i shed r e p o r t s , "Mee t ing of the I n t e r n a t i o n a l G r a v i m s t r i c C o m m i s s i o n , P a r i s , 15-19 S e p t e m b e r 1959" and " P r o v i s i o n a l G e n e r a l Repor t on Re la t ive M e a s u r e s of I n t e n s i t y of G r a v i t y on the E a r t h , 1957-1960".

T h e r e was some d i s c u s s i o n of the m o s t su i t ab le t i m i n g fo r the p r e p a r a t i o n of Na t iona l R e p o r t s on G r a v i m e t r y , in v iew Of the r e l a t i v e l y sho r t t i m e I n t e r v a l be tween the r e g u l a r l y s c he du l e d m e e t i n g s of the I n t e r n a t i o n a l G r a v i m e t r i c C o m m i s s i o n and the I . U . G . G . G e n e r a l A s s e m - b l i e s . P r o f . VENING M E I N E S Z , In p a r t i c u l a r , r e c o m m e n d e d tha t the Na t iona l R e p o r t s be p r e p a r e d jus t p r i o r to the G e n e r a l A s s e m b l i e s . The Sec t ion P r e s i d e n t no ted tha t the ques t i on of N a t i o n a l R e p o r t s would be d i s c u s s e d l a t e r b y the Exe c u t i ve C o m m i t t e e of the A s s o c i a t i o n and sugges t ed p o s t p o n e m e n t of a dec i s i on of th i s m a t t e r .

SECOND SESSION (29 July)

The Sect ion p a r t i c i p a t e d a c t i v e l y in the f i r s t s e s s i o n of the A s s o - c i a t i on S y m p o s i u m on E a r t h S a t e l l i t e s . T h i s s e s s i o n p laced s p e c i a l e m p h a s i s on the d e t e r m i n a t i o n of the e a r t h ' s g r a v i t y f ie ld f r o m o b s e r - va t ions on s a t e l l i t e s dur Ing the pas t t h r e e y e a r s . As C h a i r m a n of S . S . G . N ~ 9, Dr. W. MA2KOWITZ r e p o r t e d on the v a r i o u s d e s i r a b l e c h a r a c t e r i s t i c s of s a t e l l i t e s u s a b l e for geodet ic p u r p o s e s , and e s p e c i a l l y no ted tha t an o p t i m u m va lue of s a t e l l i t e p e r i g e e for g r a v i t y s t ud i e s a p p e a r e d to be about 500 kin , as c o n t r a s t e d to 1000-2000 km fo r g e o m e - t r i c a l app l i ca t i ons . Dur ing an ex tended d i s c u s s i o n of v a r i o u s a s p e c t s of s a t e l l i t e pos i t i on d e t e r m i n a t i o n , D r . F . L . W H I P P L E r e p o r t e d tha t B a k e r - N u n n c a m e r a o b s e r v a t i o n s on ex i s t Ing s a t e l l i t e s we re g iv ing p o s i t i o n a l a c c u r a c i e s of 70 to 100 m e t e r s . I n f o r m a t i o n a l so was r e c e i v e d that a c c u r a c y of doppler o b s e r v a t i o n s on the U .S . " T r a n s i t " s a t e l l i t e is exceed ing the o r i g i n a l e s t i m a t e s .

In r e p o r t I n g on a c t i v i t i e s ef S . S . G . N* 17 , D r . A . H . COOK d i s c u s s e d the o r b i t a l d y n a m i c s invo lved In d e t e r m i n a t i o n of the e a r t h ' s e x t e r n a l g r a v i t y f ie ld by o b s e r v a t i o n of s a t e l l i t e mot ion ; he a l so no ted tha t r e c e n t o b s e r v a t i o n s on the T r a n s i t s a t e l l i t e a p p e a r e d to c o n f i r m the t h i r d deg ree zona l h a r m o n i c t e r m as d e r i v e d f r o m p r e v i o u s s a t e l l i t e o b s e r v a t i o n s . Dr. COOK a l so d rew a t t e n t i on to the de l i ca te p r o b l e m of

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c o m p a r i n g g r av i t y data a s ob ta ined f r o m s a t e l l i t e and s u r f a c e o b s e r v a - t i o n s , and sugges ted tha t to t h i s end one migh t compute f r o m sa t e l l i t e data the v a r i a t i o n of g r a v i t y as a func t ion of p o t e n t i a l . P r o f . A . A . MIKHAILOV p r e s e n t e d a p a p e r by P r o f . I .D . ZHONGOLOVITCH which t r e a t e d the effects of v a r i o u s degree t e r m s in the h a r m o n i c e xpa ns i on of the e a r t h ' s g r a v i t y f ie ld , and inc luded an e s t i m a t e of r e l a t i v e m a g n i - tude of t he se t e r m s .

The subsequen t d i s c u s s i o n s ind ica ted a g e n e r a l a g r e e m e n t tha t s a t e l l i t e o b s e r v a t i o n s m a d e to da t e , even though of somewha t low a c c u - r a c y , have a m u c h g r e a t e r weight in d e t e r m i n i n g the e a r t h ' s shape , and e x t e r n a l g r av i t y f i e l d , t h a n does a n a n a l y s i s of the ex i s t i ng s u r f a c e gravity data.

THIRD SESSION (29 July)

In h i s r e p o r t on S. S .G. N ~ 18 (Absolute g r a v i t y d e t e r m i n a t i o n s ) , Dr . COOK noted that twe lve new abso lu t e d e t e r m i n a t i o n s of g r a v i t y have b e e n m a d e s ince 1946 o r a r e now u n d e r way. It was a l s o e m p h a s i z e d t h a t , i n addi t ion to the obvious i m p o r t a n c e of i n c r e a s e d a c c u r a c y in m e t r o l o g i c a l work , t h e r e i s a geodet ic a pp l i c a t i on in the d e t e r m i n a t i o n of the e a r t h ' s m e a n r a d i u s by m e a s u r e m e n t of the p e r i o d of r e v o l u t i o n of the m o o n , coupled with r a d a r o b s e r v a t i o n s of the m o o n ' s d i s t a n c e and the abso lu t e va lue of g r a v i t y on the e a r t h ' s s u r f a c e . A l s o , the a b s o l u t e d e t e r m i n a t i o n s migh t be u s e f u l in check ing r e l a t i v e p e n d u l u m m e a s u r e m e n t s . Dr. COOK a n t i c i p a t e d a c r i t i c a l d i s c u s s i o n of the v a r i o u s d e t e r m l n n t i o n s when a l l those now u n d e r way a r e comple t ed , and a l so no ted tha t the r e l a t i v e connec t ions be tween a b s o l u t e s t a t i ons m u s t be e x a m i n e d m o r e ca re fu l ly . It was ev iden t f r o m the r e p o r t tha t , a l though a l l the r e c e n t d e t e r m i n a t i o n s a r e not equa l ly r e l i a b l e , the b e t t e r ones a p p e a r to a g r e e wi thin one m~]ltgal .

Dur ing a f u r t h e r d i s c u s s i o n of a b s o l u t e g r a v i t y m e a s u r e m e n t s , Dr. L . G . D . THOMPSON r e p o r t e d on a new r e l a t i v e p e n d u l u m des ign tha t m a y be u sed in a n abso lu t e s e n s e by chang ing the lmtfe edges f r o m the suppor t to the p e n d u l u m , P r o f . G . P . WOOLLARD s t r o n g l y u r g e d the u se of po r t ab le abso lu t e g r a v i t y i n s t r u m e n t s . P r o f . J . C. ROSE d e s c r i b e d a p roposed e x p e r i m e n t invo lv ing a change in m a s s of a d ropped body. P rof . Y .D. BOULANGER r e p o r t e d on the m o s t r e c e n t U . S . S . R . abso lu t e g r av i t y data , g iv ing a r e s u l t a n t va l ue o f - 1 2 . 1 • 0 .58 rega l s c o r r e c t i o n to the P o t s d a m s y s t e m . P r o g r e s s r e p o r t s we re g iven on the F i n n i s h (long pendulum) and A r g e n t i n e ( r e v e r s i b l e p e n d u l u m ) a b s o l u t e d e t e r m i n a t i o n s .

In opening the d i s c u s s i o n on the t echn ique of r e l a t i v e p e n d u l u m m e a s u r e m e n t s Mr. BROWNE r e f e r r e d to h i s r e c e n t p r o v i s i o n a l m a n u a l on th i s sub jec t , and s t a t ed tha t f u r t h e r c o r r e c t i o n s or c o m m e n t s would be we lcomed p r i o r to i t s pub l i ca t ion in B u l l e t i n G6od6sique. S e v e r a l new types of f ie ld pendu lum a p p a r a t u s we re d e s c r i b e d . Of p a r t i c u l a r i n t e r e s t was the new a p p a r a t u s developed in the U. S . S . R . , which e mp l oys s ix i n v a r pendu lums swinging at a t m o s p h e r i c p r e s s u r e ; and the C a n a d i a n

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sys t em which employs bronze pendulums with e x t r e m e l y c lose con t ro l of t e m p e r a t u r e . Prof . J. BOKUN d e s c r i b e d the techniques employed in es tab l i sh ing a fundamental pendulum network in Poland by means of the A s ~ , ~ n 4 - pendulum appa ra tus with a Helmhol tz co i l for compensa t ion of the e a r t h ' s magnet ic f ield.

FOURTH SESSION (30 July)

In continuing the d i scuss ion on r e l a t i v e pendulum m e a s u r e m e n t s , Prof . ROSE p re sen t ed s l i de s showing p i c t o r i a l de ta i l s of the Gulf quar tz appa ra tus employed by the U n i v e r s i t y of Wiscons in group. A l so shown were d i s c r e p a n c i e s based on reoccupa t ions , and c o m p a r i s o n s with g r a - v i ty va lues obtained with o ther pendulums and g r a v i t y m e t e r s . This was followed by a gene ra l d i scuss ion r e l a t i ng to the con t ro l of pendulum e r r o r s , p a r t i c u l a r l y of the s y s t e m a t i c type.

P r o f . C . MORELLI r e p o r t e d the a c t i v i t i e s of S . S . G . N ~ 5 in evaluat ion of the world 1st o r d e r ne twork and noted the a v a i l a b i l i t y of the 1957 and 1959 r e p o r t s , with 1960 supplement . He s t a t ed tha t the mos t r e c e n t pendulum and g rav i ty m e t e r data had not been included, and r e q u e s t e d that t he se be furn ished as soon as pos s ib l e so tha t an ad jus tment can be m a d e . The Study Group p roposed the addi t ion of Madison, P a r m a , Oslo , and Mowbray to the 1st o r d e r n e t w o r k , and r e c o m m e n d e d the m e a s u r e m e n t of a number of add i t iona l pendulum and g r av i t y m e t e r connect ions between f i r s t - o r d e r s ta t ions .

A r e p o r t was r e c e i v e d f rom Dr. P. HERRINCK on a c t i v i t i e s of S. S.G. N ~ 5a, Technique of g r a v i t y m e t e r opera t ions . Dr. HERRINCK has inves t iga ted the t h e o r y of opera t ion of the North A m e r i c a n m e t e r and intends to c i r cu l a t e a d ra f t copy of his r e p o r t on th is m e t e r in the nea r future. In o r d e r to make poss ib l e the publ ica t ion of a comprehen- s ive monograph on g rav i ty m e t e r opera t ion , he r eques t ed that s i m i l a r in format ion on o ther types of m e t e r s be sent h im at : 166 Avenue des Pagodes , Bruxe l l e s H, Belgium.

FIFTH SESSION ( l s t August)

At the opening of the s e s s i on t h e r e was a fu r the r r e p o r t on the work of S. S .G. N ~ 5. A s p e c i a l meet ing of the Study Group had in the mean t ime been a r r a n g e d by Prof . MORELLI to d i scus s in de ta i l the p rob l em of ne twork ad jus tment and to decide f ina l ly upon the add i t iona l pendulum and g rav i ty m e t e r connect ions needed. A study of the ava i l ab l e new data indica ted a g r e e m e n t s of 0.2 to 9.3 regal with those data a l - r e a d y publ i shed in the Study Group r e po r t .

Concerning the problem of abrupt changes in pendulum period during an extensive field measurement program, Prof. MORELLI called attention to the forthcoming publication by the University of Wisconsin group of all pendulum data obtained by Dr. ROSE and associates with the Gulf quartz apparatus. He proposed to circulate a draft paper on

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th is subjgct a s soon as the data become a va i l a b l e , and sugges ted that a de ta i l ed d i scuss ion be postponed unt i l then.

Dr. WOOLLARD s ta ted tha t the va r ious in te rcon t inen ta l connec- t ions made with g r av i t y m e t e r s us ing shor t r ange d ia ls a r e in good a g r e e m e n t with his wor ld-wide g rav i ty m e t e r network. He s t r e s s e d the impor t ance of m e a s u r i n g g rav i ty m e t e r d i f f e rences on a t in,form c a l l - b ra t ion s t anda rd .

T h e r e was a gene ra l d i scuss ion of the mos t su i tab le way to ad jus t the ex tens ive wor ld 1st o r d e r network. Dr. COOK sugges ted the use of punch c a r d s with frequent r e v i s i o n s , say , e v e r y t h r e e y e a r s ; he noted that p r o p e r a s s e s s m e n t of weights is the mos t c r i t i c a l p r ob l e m in such an ad jus tment .

As the new MORELLI r e p o r t on S. S .G. N* 5 contained a r e v i s e d e s t i m a t e fo r the bes t c o r r e c t i o n to the P o t s d a m s y s t e m , the quest ion of adopt ing a defini t ive value was p laced be fore the meet ing. However , a f t e r a p r e l t r n~n tmary d i scuss ion the m a t t e r was d e f e r r e d at the sugges- t ion of the P r e s i d e n t .

P ro f . BOULANGER d e s c r i b e d the g r a v i t y m e a s u r e m e n t s c a r r i e d out in the An ta r c t i c reg ion by the group f r o m the U. S. S .R. A c a d e m y of Sc iences . These were accompl i shed by a i r p l a n e t r a n s p o r t and land t r a v e r s e s . On some of the e a r l y work the s ta t ion e leva t ions were d e t e r - mined by b a r o m e t e r with l lml t ed a c c u r a c y . However �9 on t h e r ecen t t r a v e r s e work the e levat ions were de t e r m i ne d g e o m e t r i c a l l y with m a x i - mum e r r o r s of + 2 m e t e r s . D r . WOOLLARD r e p o r t e d on the U. S. A n t a r c t i c g r a v i t y work, including in te rconnec t ion of the va r ious m a j o r g rav i ty b a s e s .

SIXTH SESSION ( l s t August)

Repo r t s were p r e sen t ed by S. S .G. N* 6 on the g r a v i m e t r i c c a - l i b r a t i on b a s e s in Europe and North A m e r i c a . Prof . KNEISSL s ta ted that the European ca l ib ra t ion base m e a s u r e m e n t s were n e a r l y comple ted and the data a r e being p r e p a r e d for ad jus tment . He p roposed that the data be fu rn i shed s e v e r a l European ins t i tu t ions to p e r m i t independent ad jus tmen t s . P ro f . HONKASALO r e p o r t e d on the pendulum m e a s u r e m e n t s in p r o g r e s s with the Cambr idge appa ra tus in no r the rn Europe , including a connect ion to Po t sdam. It was hoped that these m e a s u r e m e n t s would c l a r i f y the ex is t ing d i s c r epancy between the pendulum and g rav i ty m e t e r va lues at H a m m e r f e s t . ~ Dr . KNEISSL p r o p o s e d the ad jus tment of a European g r a v i t y m e t e r network to unify the va r ious na t iona l su rveys .

The Nor th A m e r i c a n calibra�88 base was r e p o r t e d by Mr. RICE as s a t i s f a c t o r y fo r p r a c t i c a l geodet ic work and in good a g r e e m e n t with the European s tandard . However , it was s t a ted that addi t iona l pendulum and g r a v i t y m e t e r obse rva t ions a r e needed be fore a c o m p l s t e l y s a t i s f a c - t o r y ad jus tmen t can be achieved.

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P r o f . BOULANGER r e p o r t e d tha t m e a s u r e m e n t of t he C e n t r a l A s i a c a l i b r a t i o n b a s e has b e e n d e f e r r e d pend ing d e v e l o p m e n t of n e w a p p a r a t u s . No f o r m a l p r o g r e s s r e p o r t Was g iven on the F a r E a s t c a - l i b r a t i o n b a s e ; h o w e v e r D r . W O O L L A R D s t a t e d tha t t he e x i s t i n g p e n - du lum s t a t i o n s in tha t r e g i o n p r o v i d e a g r a v i t y r a n g e o f 5500 r e g a l s .

Dr. C. MAZZON summarized his report onthe 1958-59 pendulum measurements over the European calibration llne between Hammerfest and Catania. This was accomplished with the new three-pendulum appa- ratus developed by the Italian Geodetic Commission. The epparatus e m p l o y s m o l y b d e n u m p e n d u l u m s of t he m~n~mum type wi th p h o t o - e l e c t r l c recording and quartz clock time control

SEVENTH SESSION (2 Augus t )

This session Was arranged in cooperation with Section V (Geoid) primarily to discuss possibilities of the new gravimetrlc techniques in improving world-wide coverage for geoid studies.

Dr. WOOLLARD described the world-wide pendulum and gravity meter base network established by the University of Wisconsin group over a 5000 regal range, with an indicated average discrepancy of ~: 0.4 r egaL

Dr . W O R Z E L p r e s e n t e d a c o m p r e h e n s i v e r e p o r t of t h e w o r k of S . S . G . N ~ 2 0 , G r a v i t y m e a s u r e m e n t s a t s e a . T h i s r e p o r t i n d i c a t e d good p r o g r e s s t o w a r d the p e r f e c t i o n of s u r f a c e sh ip m e t e r s f o r r o u t i n e o p e r a t i o n a l u s e , p a r t i c u l a r l y in the c a s e of t he L a C o s t e - R o m b e r g and G r a f t y p e s . Of s p e c i a l i n t e r e s t was a s u p p l e m e n t a r y a n n o u n c e m e n t b y Dr . B . J . C O L L E T T E tha t the N e t h e r l a n d s G e o d e t i c C o m m i s s i o n e x p e c t s to conduc t i n i t i a l t e s t s on a t owed s e a g r a v i t y m e t e r w i th in abou t one y e a r .

A f t e r s o m e d i s c u s s i o n the Sec t ion a p p r o v e d in p r i n c i p l e a r e c o m - m e n d a t i n n b y S. S .G . N ~ 20 def~-~ng a s y s t e m a t i c p r o c e d u r e f o r c o n n e c - t i ng s e a p o r t s t a t i o n s g r a v i m e t r i c a l l y to the w o r l d 1st o r d e r n e t w o r k .

Dr . TSUBOI r e p o r t e d on the d e v e l o p m e n t of h i s o s c i l l a t i o n t y p e b i f i l a r s e a s u r f a c e g r a v i t y m e t e r . V e r t i c a l s t a b i l i z a t i o n i s a c h i e v e d by an a c c e l e r o m e t e r - s e r v o s y s t e m o p e r a t i n g in c o m b i n a t i o n wi th a w h e e l of h igh r o t a t i o n a l i n e r t i a . A t e s t of t h i s i n s t r u m e n t was c a r r i e d out in e a r l y 1960 on a c r u i s e b e t w e e n Y o k o h a m a and San F r a n c i s c o ; a l t hough g r a v i t y cou ld not be m e a s u r e d u n d e r h e a v y s e a c o n d i t i o n s , t he t e s t p r o v i d e d da t a e x p e c t e d to be u s e f u l in f u r t h e r r e f i n e m e n t o f the i n s t r u - m e n t .

A e r i a l g r a v i t y m e t e r t e s t s wi th a L a C o s t e - R o m b e r g i n s t r u m e n t w e r e d e s c r i b e d b y Dr . L . G . D . THOMPSON of U . S . A i r F o r c e C a m b r i d - ge R e s e a r c h C e n t e r . The i n i t i a l t e s t s conduc t ed in N o v e m b e r 1958 in a h i g h - a l t i t u d e j e t a i r c r a f t d e m o n s t r a t e d the f e a s i b i l i t y of ob t a in ing 5 - m i n u t e a v e r a g e g r a v i t y r e a d i n g s wi th a n a c c u r a c y of 10 r e g a l s .

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COMPTE Rs DF_.S REUNIONS DE LA SECTION IV - GRAVIMI~TRIE

E x p e r i m e n t a l work was r e s u m e d e a r l y in 1960, the i n s t r u m e n t be ing moun ted in a C-130 ( j e t - p r o p ) a i r c r a f t . F l igh t t e s t s we re made at Edwards A i r F o r c e B a s e , C a l i f o r n i a , at a l t i t udes of. 7, 14, 17, and 30 thousand feet . F u r t h e r t e s t s were conducted in the f o r m of a r e g i o n a l s u r v e y ove r a known s u r f a c e g r a v i t y f ie ld in the s o u t h - c e n t r a l U.S . ; the fl ight p a t t e r n s c o v e r e d an a r e a of 400 x 175 m i l e s , with p r o f i l e s spaced at 2 5 - m i l e i n t e r v a l s . P r e c i s e nav iga t ion was ob ta ined by H i r a n o b s e r v a t i o n s and p h o t o g r a m m e t r i c con t ro l . It was appare~lt tha t if t h i s s y s t e m can be b rought to a n o p e r a t i o n a l s t a t u s , it will p rov ide m e a n g r av i t y va lues for s q u a r e s u b d i v i s i o n s of the e a r t h ' s s u r f a c e , f i l l ing out ex i s t ing gaps and enab l ing m o r e a c c u r a t e geoid s tud ies . T h e r e was extended d i s c u s s i o n of the v a r i o u s t h e o r e t i c a l p r o b l e m s i n h e r e n t in such a s y s t e m . The p r a c t i c a l d i f f i cu l t i es of d e t e r m i n i n g a i r c r a f t m o t i o n , r a t h e r than l i m i t a t i o n s of the m e t e r i t s e l f , a p p e a r e d to be the m o s t c o n t r o v e r s i a l a spec t .

Dr. J . C . HARRISON d e s c r i b e d the s u c c e s s f u ] ~ s e r i e s of m e a s u r e - m e n t s made with the L a C o s t e - R o m b e r g s u r f a c e ship g r a v i t y m e t e r by the Ins t i t u t e of Geophys i c s of the U n i v e r s i t y of C a l i f o r n i a be tween O c t o b e r 1958 and D e c e m b e r 1959. On a 3 0 0 - m i l e t r a c k off s o u t h e r n C a l i f o r n i a , c o m p a r a t i v e m e a s u r e m e n t s with 13 s u b m a r i n e g r a v i t y s t a t ions gave a RMS d i s c r e p a n c y of f 4 . 4 . m g a l . F u r t h e r c o m p a r i s o n s a g a i n s t data f r o m u n d e r w a t e r m e t e r s du r ing a s u r v e y of the Gulf of L o w e r C a l i f o r n i a in 1959 ind ica ted an a c c u r a c y of about 2 m g a l s fo r the s u r - face m e t e r . L a t e r , an i n t e n s i v e s u r v e y was conducted o v e r an a r e a of about 35 ,000 s q u a r e m i l e s of fshore f r o m sou the rn Ca l i fo rn i a . It was found p o s s i b l e to ob ta in m e a s u r e m e n t s fo r about 50 % of the o p e r a t i o n a l pe r iod in sh ips of d i s p l a c e m e n t up to 505 g r o s s tons . Dr. HARRISON announced that the s a m e g r a v i t y m e t e r , but with i n c r e a s e d damping , wi l l be employed d u r i n g the p e r i o d Augus t 1960 - F e b r u a r y 1961 on the "Monsoon" expedi t ion of the ARGO, about 1300 tons d i s p l a c e m e n t . The rou te is : San Diego-New G u i n e a - A u s t r a l i a - M a u r i t i u s - T a h i t i - S a n Diego.

M r . O . W . WILLIAMS of U.S . A i r F o r c e C a m b r i d g e R e s e a r c h C e n t e r d e s c r i b e d new g r a v i t y m e t e r s be ing developed by tha t o r g a n i z a t i o n for m e a s u r e m e n t s on ice i s l a n d s , r e m o t e l y f r o m h e l i c o p t e r s , and in u r b a n c e n t e r s u n d e r s e v e r e v i b r a t i o n cof~ditions.

EIGHTH SESSION (2 August)

The p r o c e e d i n g s were d i r e c t e d m a i n l y to t h e o r e t i c a l a s p e c t s of the p e r f o r m a n c e of new g r a v i t y m e a s u r i n g i n s t r u m e n t s , a s a f fec ted by v a r i o u s types of a c c e l e r a t i o n s e n c o u n t e r e d in su r f ace v e s s e l s and a i r - c raf t .

P r o f . MORELLI r e p o r t e d on r e c e n t sea su r f ace m e a s u r e m e n t s with a G r a f m e t e r . Dr. HARRISON p r e s e n t e d a c o m p r e h e n s i v e t r e a t - m e n t of the t h e o r e t i c a l a s p e c t s of sea g r a v i t y m e t e r s , of both the s t ab le p l a t f o r m and swing ing g i m b a l types . He s t r e s s e d the i m p o r t a n c e of the c r o s s coupl ing effect , p roduced by h o r i z o n t a l and v e r t i c a l a c c e l e r a t i o n s ac t ing in such phase r e l a t i o n s h i p as to p roduce a m o r e or l e s s c i r c u l a r

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m o t i o n of the i n s t r u m e n t . Dr. WORZEL s t a t ed tha t h i s m e a s u r e m e n t s with the G r a f m e t e r did nod ind ica te a c r o s s coupl ing ef fec t , and that the c i r c u l a r m o t i o n t h e o r y would not app ly i f the phase a n g i e s v a r i e d in r a n d o m fash ion . Dr. HARRISON r e p l i e d tha t s e r i o u s c r o s s kcoupling might r e s u l t when long swel l condi t ions a r e e n c o u n t e r e d .

Mr. BROWNE d e s c r i b e d r e c e n t t e s t s with a G r a f s u r f a c e ship m e t e r be tween Eng l and and G i b r a l t a r , and in the M e d i t e r r a n e a n . U n d e r c a l m sea cond i t ions in the M e d i t e r r a n e a n , 700 m i l e s of t r a v e r s e were r u n p a r a l l e l to the A f r i c a n coas t with an i nd i ca t ed a c c u r a c y of + 2 m g a l s . On 200 m i l e s of t r a v e r s e in the At lan t i c u n d e r F o r c e 3 s e a cond i t ions and m o d e r a t e swe l l the a c c u r a c y was c o n s i d e r a b l e l e s s . M r BROWNE d e s c r i b e d the p r o c e d u r e employed fo r eva lua t i ng m e t e r p e r f o r m a n c e by r u u n i n g the v e s s e l in opposi te d i r e c t i o n s o v e r a f ixed g e o m e t r i c a l p a t - t e r n , the n a v i g a t i o n be ing obta ined by r a d a r o b s e r v a t i o n s on a n a n c h o - r e d buoy. In conc lud ing , he s t r e s s e d the need fo r an i n e r t i a l nav iga t i on s y s t e m which would give t r u e v e l o c i t i e s to 0 . 2 5 knot.

P r o f . BOULANGER r e p o r t e d on de ve l opme n t of a 6 - p e n d u l u m quartz system and a quartz gravity meter system. These are used in combination on surface ships and give accuracies of 1.5-2.0 and 2.5- 3.0 regals, respectively. Experimental tests of the gravity meter have been conducted in the North Sea.

NINTH SESSION (3 August) '\

The President opened the session by summarizing the published report just received from Prof. TARDI on the functioning of the Inter- national Gravimetric Bureau. The new address of the Bureau is 39ter rue Gay Lussac, Paris (V~ The Section expressed sincere thanks to Prof. TARDI for his excellent report.

In discussing Antarctic gravity measurements Dr. WOOLLARD noted that by far the greatest difficulty was encountered in determining station elevations. This tends to delay seriously the publication of gra- vity anomaly data, as the elevations depend on barometric measurements which must be carefully correlated with weather soundings. Dr. WOOL- LARD r e p o r t e d that a l l g r a v i m e t r i c data ob ta ined t h r ough the 1958 s e a s o n have b e e n p r o c e s s e d . Mr. BROWNE sugges ted tha t g r a v i t y be m e a s u r e d r e p e a t e d l y a t the s a m e s i t e s , b e g i n n i n g e a r l y in the h i s t o r y of A n t a r c t i c o p e r a t i o n s , to help def ine v e r t i c a l m o v e m e n t s of the ice su r f ace .

P rof . KNEISSL u r g e d that any changes in wor ld 1st o r d e r s t a t ion s i t e s be p r o m p t l y r e p o r t e d to the I n t e r n a t i o n a l G r a v i m e t r i c B u r e a u . The i m p o r t a n c e of r e l i a b l e e x c e n t e r s for the 1st o r d e r s t a t i o n s was e m p h a - s ized . T h e r e was extended d i s c u s s i o n on whe the r a new 1st o r d e r s ta t ion s i te should be s e l e c t e d if the o r i g i n a l s i te is d e s t r o y e d . A f t e r a fu l l exchange of v i e w s , i t was decided by vote of the Sec t ion t ha t the o r i g i n a l s i t e should be r e t a i n e d a s the p r i m a r y r e f e r e n c e point .

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COMPTE RENDU DES REUNIONS DE LA SECTION IV - GRAVIM~TRIE

The President proposed and the Section approved continuation of the existing Special Study Groups. However, it was anticipated that functioning of S.S.G. N ~ 17 on earth satellites might-be modified or terminated through the establishment by the Association of a Commission on Earth SatelLites. ALso, it was decided to expand the scope kof S.S.G. N ~ 20, Gravity measurements at sea, to include techniques of observation.

TENTH SESSION (4 August)

After minor revisions, "the Section approved 11 recommendations for submission to the Association. No agreement could be obtained on a proposal to define in specific terms the best present correction to the Potsdam system. The 1960 MORELLI report on S. S.G. N ~ 5 had pro- posed a mean value of -12.8 • 0.3 regals for the correction, based on an available data. Adoption of this value, or a llke specification, was strongly urged for practical reasons by several persons, particularly Prof. BOULANGER and Prof. KNELSSL. Dr. COOK was strongly opposed to a precise definition under the circumstances, and stated that without a thorough study of the experiments, particularly with respect to syste- matic errors, it would be impossible to derive a reLiable value and estimate of precision. He further recommended that silch a study should be carried out by a group of specialists in metrology and that the findings be made in concurrence with the Bureau of Weights and Measu- res. At the suggestion of Prof. VENTNG IVIEINESZ, the Section decided to take no affirmative action on this question.

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