temperature sensor pairs ... - IEEE Xplore

AN IMPROVED SALARGOS BUOY FOR DEPLOYMENTS I N POLAR SEAS Samuel P. Burke P o l a rR e s e a r c hL a b o r a t o r y C a r p i n t e r i a ,C a l i f o r n i a

D r . James M o r i s o n P o l a rS c i e n c eC e n t e r ,A p p l i e dP h y s i c sL a b o r a t o r y UniversityofWashington Seattle,Washington

ABSTRACT An improvedoceanographic and m e t e o r o l o g i c a l d a t ac o l l e c t i o n buoy system called SALARGOS has been developed fod r e p l o y m e n t si np o l a sr e a sf o r p e r i o d so u f pt ot w oy e a r s R . ecenA t rctic d e p l o y m e n tws e rm e a dues i nsgp abru o yws i t h 300 m e t esre n s osrt r i n g s each equipped w i t hs i x t e m p e r a t u r e / c o n d u c t i v i t y s e n s o rp a i r s D . a t ar e l a y ARGOS c a p a b i l i t yo ft h e i sc a r r i e do u tu s i n gt h e t w o o r b i t i n g NOAA Sate1 1 i t e s . The d a t a t h r o u g h p u t a v a i l a b l ei nA r c t i cr e g i o n sf r o mt h et w o s a t e l l i t e sp r o v i d e sf o hr i g hs a m p l i n gr a t e s when c o m p a r e dt ob u o y sd e p l o y e d i ne q u a t o r i a ls e a s . F o r t ys a l i n i t yp o i n t sa r ec u r r e n t l yb e i n g c o l l e c t e de v e r yh o u r T. h r e eA r c t i cb u o y sa r e c u r r e n t l py r o v i d i n dg a t taso t u d iyn t e r n a l wave a c t i v i t ya sp a r to ft h e MAVOCEANO A r c t i cB u o y Program.

INTRODUCTION The developmentofthe SALARGOS buoybegan in 1 9 8 0T. h eo b j e c t i v eh a b s e e nt oc r e a t ea n i n s t r u m e n ts y s t e mc a p a b l eo fm a k i n gu n a t t e n d e d hydrographic measurements i n remote areas o ft h e A r c t i c Ocean. The f i r s t buoyemployedthree SeaB i r dt e m p e r a t u r e and c o n d u c t i v i t ys e n s o rp a i r sa t f i x e dd e p t h st o 50m. It was t e s t e da t h e FRAM I 1 1 i c e camp i n1 9 8 1 a, n dt e s t e da g a i n s t h y d r o c a s t sd u r i n g a four-monthdeployment a t Pond I n l e t N.W.T. i n 1982. A s e c o n db u o y w , i t hs i x s e n s o rp a i . r s ,w a sb u i l ti n1 9 8 2a n du s e da t Fram IV i n 1982 and d u r i n g M I Z E X 83. Both buoys c o m p u t e3d- h o ua rv e r a g eot sef m p e r a t u raen d c o n d u c t i v i t y and t r a n s m i t t e dt h e s ev i at h e ARGOS system.Thesebuoys a r ed e s c r i b e di nM o r r i s o n ,e t al.11982). T hsee c o ngde n e r a t i o n SALARGOS buoy was developed i n o r d e r t o make long-termmeasurements of i n t e r n a l wave energy i nt h eA r c t i c . Much of thebuoyhardwarefromthefirst SALARGOS buoy was u s e db, utth e m i c r o p r o c e s s osr o f t w a r e was e x t e n s i v em l yo d i f i e ttroda n s mi ni ts t a n t a n e o u s samplesgatheredevery12minutes.High-frequency samplinga1lowsthedatatobeconvertedto spectraofverticaldisplacementinthelowto m e d i u m - f r e q u e n c yb a n do ft h ei n t e r n a w l ave spectrum. A s i d eb e n e f ii tsh a t , due t o cable m o t i o ns, a m p l e sa r eo b t a i n e da t a v a r i e t yo f depths above the free-hanging sensor depths: SO, f ot rhpeu r p o soemf e a s u r i nhgy d r o g r a p h ys,h o r t segments o ft e m p e r a t u r e and s a l i n i t yp r o f i l e sa r e obtained.

CH2498-4/87/0000- 49

I n 1985 t h e f i r s t o f t h i s buoytype was d e p l o y e adt th A e r c t i Icn t e r n a l Wave Experiment camp i nt h eB e a u f o r t Sea. It c o n t i n u e dt oo p e r a t e f o r o v e r a year. The t h i r dg e n e r a t i o n of SALARGOS buoy uses t h e same d a t aa c q u i s i t i o ns c h e d u l ef o rt h e o c e a n o g r a p h i dc a t a b u t u s e s b u o ye l e c t r o n i c s h a r d w a r ei d e n t i c a tl ot h a dt e v e l o p e df o rt h e PRL TOGA b u o yp r o g r a mo ft h eN a t i o n a lD a t aB u o y C e n t e( rK o z a8k5 T ) .h inse hwa r d w a rhea s u n d e r g o ne ex t e n s i q v eu a l ict oy n t rsocl r e e n i n g , r e s u l t i n igen x t r e m e l lyo w f a i l u r rea t e s . A d e t a i l e da t - s e ap e r f o r m a n c ea n a l y s i so f a field of 67 PRL b u i It TOGA b u o y s was r e c o n s t r u c t e d f r o m NDBC's weeklyDataPlatformStatusReports.Data r e p o r t sf o r 1.5 y e a r sw e r ea n a l y z e d ,r e s u l t i n gi n a t o t a lo p e r a t i n gl i f eo f 14.839days w i t h a mean timetofailureof 4.5 y e a r s f o r b u o y s t h a t s t o p p e dr e p o r t i n gt o ARGOS. The new b u o y sa l s o make measurements obf a r o m e t r i cp r e s s u r e and a i r temperature. TECHNICAL DETAILS 1 The SALARGOS b u o yi l l u s t r a t e di nF i g u r e 8 i n c hd i a m e t e r c o n s i s t so f a 1 4f o o tl o n g a l u m i n u mt u b ei c eh u l w l eighing 197poundsloaded witb h a t t e r i e as n e dlectronics. A 3 0m 0 eter m u l t i c o n d u c t ocra b lhea n g i nbge l o twhbeu o y c o n t a i n s s i x conductivity/temperature s e n s o rp a i r s a t 15, 50, 100. 150, 200 and250metersbelowthe w a t e rl i n ew i t h a P a r o sd e p t hs e n s o ra t 250 meters. The c a b l ei s 1.35cm i nd i a m e t e r and has 39 each No. 24 conductors. An i n n e cr o r eo f A k e v l aprr o v i d et sh e 3.2kg b r e a k i nsgt r e n g t h . l i g h dt a c r o nb r a i dc o v e r ts h e l e c t r i c a l conductors. a 10cm d i a m e t e2r 9 k sg t e e l c y l i n d r i c a lw e i g h ti sp o s i t i o n e da tt h eb o t t o mo f t h es t r i n g . A s e r i e so ft e n 30cm d i a m e t e rn e t f l o a t sa r ep o s i t i o n e da tt h et o po ft h ec a b l et o p r o v i d ee n o u g hr e s e r v eb u o y a n c yf o r a 61cm freeboard.

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FIGURE 2.

DIGIQUARTZ PRECISION DEPTH SENSOR

P is I no p e r a t i o n , a p r e s e n tc o u n t s t o r e di na n 8 b i t down c o u n t e ru n d e rp r o g r a m A s t a r pt u l s er e s e t st h e1 6b i t control. a c c u m u l a t o r .e n a b l e st h e down c o u n t e ra n ds e t st h e g a t ef l i pf l o p . Once t h eg a t ei s open, t h ec l o c k p u l s e sa r ep a s s e d t o t h e1 6b i tc o u n t e ra t a 1.3824 Mhz r a t e . The g a t er e m a i n s open w h i l et h e f r e q u e n c yi n p u tf r o mt h es e n s o rd e c r e m e n t st h e p r e s ect o u n t eur n t itlh ec o u nrte a c h e sz e r o . At t h i st i m et h eg a t ef l i pf l o p i s r e s e ta n dt h e s t r e a mo cf l o c kp u l s e st ot h ea c c u m u l a t o r t e r m i n a t e s . The c o u n t e r c o n t e n t s a r e now a v a i l a b l e f o r e t r i e v a bl yt h eb u o yp r o c e s s o r . The c o u n t N i sr e l a t e dt ot h es e n s o rf r e q u e n c y F s by t h e f o l l o w i n ge q u a t i o n :

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FIGURE 1. S a l a r g o sC r o s sS e c t i o n

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The conductivity/temperature s e n s o r p a i r s a r e a t t a c h e dt ot h ek e v l a rc a b l ei np o l y u r e t h a n e f a i r e df i x t u r e s shown i nt h ep h o t o oFf i g u r e 2. T h ef i x t u r e sa r eb o n d e dd i r e c t l yt ot h ec a b l e and p r o v i d ef o uflr e ea t t a c h m e npt o i n t fso trh e sensors.Heavydutynylon t i e sh o l dt h e packages f a s tt ot h eh o u s i n g s .L i g h ts h i e l d s made f r o m aluminumandpaintedwithmarineantifoulingpaint a r e shownmounted a t eachend o ft h ec o n d u c t i v i t y s e n s osr h r o u dw h i c hc o v e r tsh eB e c k m a ng l a s s c e l l .T h ep u r p o s eo ft h el i g h ts h i e l d s is to r e d u c et h el i g h ta r r i v i n ga tt h eg l a s sc e l l , with t h ea i mo fr e d u c i n gb i o f o u l i n g .

Fs= 16Fc(P-l)/N Fc i s t h e c l o c k f r e q u e n c y and P i s t h e p r e s e t count. A s a ne x a m p l e ,w i t ho n eo ft h e c o n d u c t i v i tsye n s o r s (SN.273) a t 26 mmho/cm and -1.7"C t h eo u t p u tf r e q u e n c yi s 8100.0 Hz, r e s u l t i n g i n a c o u n t N o f 434176 o r 6*216 40960 s i n c teh a e c c u m u l a t ocr a o n n l hy o l 2 d16 =65536, t h e 6 i s t h en u m b e ro of v e r f l o w st h a t h e a c c u m u l a t ho aresx p e r i e n c eFdto.hroi sv e r f l o w v a l u e ,t h ec o n d u c t i v i t y window f a l l s between22.85 and32.66 mmho/cm. T h i s r e s u l t s i n a r e s o l u t i o n o f Z X ~ O -mmho/cm. ~ If t h e windowcauses t h eo v e r f l o w t o appeaw r i t h i nt h er a n g e of i n t e r e s t t, h e nt h e v a l u eo f P may b ea d j u s t e dt os u i t . The v a l u eo f

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4 illustrates the The b l o c k d i a g r a m o f F i g u r e m a j o rs y s t e mb l o c k sm a k i n gu pt h e SALARGOS e l e c t r o n i c sT. hpee r i ocdo u n t eorp e r a t etso providedatatodeterminetheprecisefrequencyof t h et e m p e r a t u r e ,c o n d u c t i v i t y and p r e s s u r es e n s o r s by s e l e c t i n g a f i n i t e number oifn p uftr e q u e n c y z e r oc r o s s i n g st os e t a h i g hf r e q u e n c yc l o c kg a t e w h i c hi n p u t s a p u l s e t r a i n t o t h e 16 b i t a c c u m u l a t o ra si l l u s t r a t e di nt h es c h e m a t i co f F i g u r e 6.

50

P i s 1 6 0u s i n gt h ec u r r e n st e r i e so Sf e a b i r d c o n d u c t 1 v it y o s c i 1 l a t o r s . The t e m p e r a t u r e s e n s o r s and t h eD i g i q u a r t zd e p t hs e n s o ra r es a m p l e du s i n g t h e same t e c h n i q u e w i t h P=140 and18 r e s p e c t i v e l y . T h i rs e s u l t isn a t e m p e r a t u r ree s o l u t i o on f 8 ~ 1 0 - ~ " and C a depthresolutionof 0.18 meters.

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Barometrip c r e s s u r ei m s e a s u r e de v e r y 1 2m i n u t es a m p l ep e r i o du s i n g a 4 5s e c o n dg a t e period. The g a t tei m iebs a s e d on c o u n t i nogn e second i n t e r r u p t sd e r i v e df r o m a 32 kHz crystal oscillator. T hDei g i q u a r tsze n s ot yr p i c a l l y o u t p u t s a f r e q u e n c y o f 3 6 k H z .T os c a l et h e p r e s s u r ed a t a it i s nec-essary t od i v i d e down t h e 32. T h er e s u l t i n gp u l s et r a i ni s o u t p u tb y a c c u m u l a t e dd u r i n gt h eg a t ep e r i o da n dt h et e n l e a s ts i g n i f i c a n tb i t sa r er e p o r t e d on t h e ARGOS datastream. To d e t e r m i n et h ep r e s s u r e ,f i r s tt h e count i s c o n v e r t e d t o a g a t ep e r i o da n da p p l i e dt o a s e r i e s o f e q u a t i o n ss u p p l i e db yt h e m a n u f a c t u r eTr h.s e n s toerm p e r a t uairsne i m p o r t a n itn p u t ot h ed a t ar e d u c t i o ne q u a t i o n s . T h i st e m p e r a t u r ei so b t a i n e df r o mt h ei n t e r n a l h u ltle m p e r a t u r es e n s o lro c a t e dw i t h i n a few cm o ft h eb a r o m e t e r on t h eb a c ks i d eo fb u o y e l e c t r o n i c rsa c k . The barometer i s shown i nt h e p h o t o of F i g u r e 3.

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FIGURE 4. SalargosBlockDiagram

T h ep o w e rb u d g e tf o rt h e SALAKGOS b u o y i s 6. The i l l u s t r a t e d i n t h ep i ec h a r to fF i g u r e c o m p u t ecr o n t r o l l eirst h em a j o r power d r a i n on t hsey s t e m Im . p r o v eadl k a l i n e D c e l lws e r e i n t r o d u c e dr e c e n t l y and a r ec u r r e n t l yb e i n gu s e d i nt h es t a n d a r d 7.5 i n c hb a t t e r py a c k s . The new c e l l s p r o v i d e an a d d e d 40% o v e rt h ep r e v i o u s D c e l al v a i l a b l ee n e r g y . As a result?,theneartwo y e a rb u o yl i f ei so b t a i n a b l eu s i n g1 4b a t t e r y p a c k sc u r r e n t l yr a t e da t 21amperehours.

FIGURE 3. E l e c t r o n i c sC a r d

Air t e m p e r a t u r e i s measuredusing a p r e c i s i o n t h e r m i s t o sr e n s o m r ounted in a v'entilator p o s i t i . o n e d on t o po ft h ea n t e n n ah o u s i n g .T h e v e n t i l a t o rr e d u c e se r r o r sr e s u l t i n gf r o ms o l a r r a d i a t i o n o nt h es e n s i n ge l e m e n tw h i l ep r o v i d i n g a f r e ef l o wo fa i r . The s e n s o rs i g n a li sd i g i t i z e d u s i n g a 12 b i t A/D c o n v e r t e r and t h e ns c a l e dt oa n 8 b i tw o r dw h i c hi sr e p o r t e di nt h e ARGOS d a t a s t r e a m .T h eh u l tl e m p e r a t u r ei sm e a s u r e di n a s i m i l a rf a s h i o n .

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DEPLOYMENT RESULTS FIGURE 7. P o s i t i o n s o f SALARGOS b u o y s i n t h e A r c t i c Ocean a s o f AprilI, 1987.

Arcticdeploymentsof the improved %LARGOS b u o y hs a v eb e e nc a r r i e do u t i n 1984and1985 r e s u l t i n g i n fourlong term buoy d r i f t s . The two prototype buoysdeveloped f o r the Fram I11 and the Pond I n l e te f f o r t s wereupgradedwithone of t h e buoysredeployedintheBeaufortSea i n 1983 and r e b a t t e r i e d for a second year i n t h e 1984. The secondoriginalprototype was upgraded w i t h 16 b i t temperatureand an improveddepthsensor, i t was r e d e p l o y e d i n t h e A r c t i c i n 1985. The two new buoys w i t h the addedmeteorologicalsensorswere t h e s p r i n go f1 9 8 6a n da r e d e p l o y e dd u r i n g c u r r e n t l y r e p o r t i n g on t h e ARGOS system.

F i g u r e 7 shows t h ep o s i t i o n so f SALARGOS buoys 1895, 1896, and 1897 on A p r i l 1, 1987. Buoy 1 8 9 5i s a secondgenerationbuoyandwas "W. d e p l o y e d i n A p r i lo f1 9 8 6a t7 3 . 5 " N ,1 6 1 Buoys1896and1897 a r eo f t h e l a t e s t t y p e and weredeployed i n September1986near 73.5"N. 140"W and 87.75"N. 2"W r e s p e c t i v e l y .

52

23

24

25

26

27

28

SIGMA-T FIGURE 8.Sigma-tversusdepthfor a l ls i xs e n s o r p a i r s o f SALARGOS 1896 f o r t h e monthof November 1986. The buoy was n e a r 74"N, 144"W a t t h e t i m e .

An example o ft h et y p eo fh y d r o g r a p h i cd a t a a v a i l a b l ef r o mt h eb u o y si si l l u s t r a t e db y F i g u r e 8, T h eF i g u r es h o w st h eS i g m a -vt a l u e s (Sigma-t i s 1000*(water density-1.0) where water d e n s i t yi si n g m / c m * * 3c)o m p u t e fdr o m the with t e m p e r a t u raensda l i n i tdya tgaa t h e r e d SALARGOS buoy 1896 i n November o f 1986 n e a r 74"N 1 4 4 " W T. h e r e i s a c l u s t e ro fd a t ap o i n t s a s s o c i a t e dw i t he a c ht e m p e r a t u r e and c o n d u c t i v i t y s s n s opr a i r . Because the sensors move v e r t i c a l l y ;.)hen w a t e rc u r r e n t sa c to nt h ec a b l e ,t h ed e p t h cf t h eb o t t o ms e n s o ri s measured and a s i m p l ec a b l e model IS used t o e s t l m a t e t h e d e p t h o f e a c h o f t h e o t h e rs e n s o r s . Thus a c l u s t e r o f p o i n t s i n Sigma-t a n dd e p t h i s p r o d u c e d .T h ev e r t i c a lm o t i o ni s i t i m p r o v et shdee p t h b e n e f l c i able c a u s e r e s o l u t i o no ft h ea v e r a g ep r o f i l e . The c a b l e model was checked by comparingtemperature and s a l i n i t y p r o f i l e sf r o mt h e SALARGOS b u o yd e p l o y e da t AIWEX w1 t h t h e i c e camp CTD p r o f ] l e s andgoodagreement was foundbetweenthetwosystems. In g e n e r a l ,t h e SALARGOS measurementsareaccurate t ob e t t e rt h a n O . O 2 " C , 0.02 p p ta, n d 0.2m depth. The Sigma-t p r o f i l eo fF i g u r e 8 i s i n agreement w i t hp r e v i o u s m e a s u r e m e n t s i n t h e same r e g i o n T . h es p u r so f h i g h e rS i g m a - vt a l u e se x t e n d i n gf r o mt h em a i n c l u s t e ra t 200m and 250111 a r es u g g e s t i v eo fa n e d d y T. h e s ep e r t u r b a t i o n sa r es t i lbl e i n g examined.

ACKNOWLEDGMENTS W o r kw a s u p p o r t e db y ONR c o n t r a c t s N O 0 0 1 4 - 8 4 - C - 0 1 1a1nNd0 0 0 1 4 - 8 5 - C - 0 0 5a2n d NAVOCEANO c o n t r a c t N00024-85-C-6264. We w i s tho t h a n kK a t eB a d e rf o rp e r f o r m i n gt h eb u o yd a t a analysis programming and Roger Andersen f o hr i s e f f o r t sd u r i n gt h eb u o yd e p l o y m e n t s . The c o n t i n u e d Mr. George L e i d i g and MikeZikaof PRL s u p p o r tb y duringthedevelopmenteffort was n o t a b l e . REFERENCES

53

I.

M o r r i s o n , J. and Burke, S.P. eet "l S a l a r g o s T e m p e r a t u r e - C o n d u c t iv i t y BUOYS"Oceans82 C o n f e r e n c eS, e p t e m b e1r 9 8 2W , ashington, DC pp. 1255-1260

2.

Kozak, R.P. e t e l "The r o l e o f d r i f t i n g i nt h et r o p i c a l oceanglobalatmosphere program" Proceedings Oceans 85, pp 1317-1325

buoys (TOGA)