nuevas técnicas radiométricas y mediciones constantes solares

7/27/2019 Nuevas tcnicas radiomtricas y mediciones constantes solares

1/9

Solar Energy, V o l . 1 4, p p . 2 0 3 - 2 1 I . P e r s a m o n P r e s s , 1 9 7 3 . P r i n t e d i n G r e a t B r it ai n

NEW RADIOMETRIC TECHNIQUES ANDSOLAR CONSTANT MEASUREMENTS*

R . C . W I L L S O N t -(Received 10 M ay 1 9 7 1 )

A I m t r a e t - A s e r i e s o f a b s o l u t e ca v i t y r a d i o m e t e r s , d e s i g n e d t o m e a s u r e s o l a r ir r a d i a n c e , h a s b e e n d e v e l o p e da t t h e J e t P r o p u l s i o n L a b o r a t o r y . A n a l y s i s i n d i c a t e s t h e a b s o l u t e u n c e r t a i n t y o f i r r a d i a n c e m e a s u r e m e n t sm a d e b y t h e m o s t r e c e n t d e v i c e s t o b e l e s s t h a n -+ 0 . 5 m W / c m 2.I n a s e r i e s o f e x p e r i m e n t s t h e r a d i o m e t r ic s c a l e d e f i n e d b y t h e J P L i n s t r u m e n t s h a s b e e n c o m p a r e d w i t ht h e I n t e r n a t i o n a l P y r h e l i o m e t r i c S c a l e ( I P S ) . A s y s t e m a t i c 2 . 2 p e r c e n t d if f e r e n ce h a s b e e n o b s e r v e d w i t h t h eI P S p r o d u c i n g c o n s i s t e n t l y l o w e r m e a s u r e m e n t s .T h e s o l a r c o n s t a n t a n d s p e c t r a l d i s t ri b u t i o n h a v e b e e n d e r i v e d f r o m h i g h - a l t it u d e b a l l o o n f li gh t m e a s u r e -m e n t s m a d e b y t w o t y p e s o f J P L c a v i t y ra d i o m e t e r s . M e a s u r e m e n t s a t 2 5 k m i n 1 9 6 8 p r o d u c e d a s o l a rc o n s t a n t v a l u e o f 1 37 .0 m W / c m 2. F r o m 1 9 6 9 m e a s u r e m e n t s a t 3 6 k i n , a v a l u e o f 1 3 6 . 6 m W / c m 2 w a s d e r i v e d ,w i t h a n e s t i m a t e d a b s o l u t e u n c e r t a i n t y o f + -0 . 5 p e r c e n t . T h e s o l a r s p e c t r u m i n f o r m a t i o n f r o m t h e s e e x p e r i -m e n t s a g r e e s m o s t c l o s e ly w i t h t h e s o l a r s p e c t r u m m o d e l o f L a b s a n d N e c k e l .R ~ s u m ~ - L e l a b o r a t o i r e d e P r o p u l s i o n p a r R 6 a c t i o n ( J P L ) a d 6 v e l o p p ~ u n e s 6 r i e d e r a d i o m ~ t r e s a b s o l u s i tc a v i t6 , d e s t i n 6 s i t m e s u r e r l e r a y o n n e m e n t s o l a ir e . L ' a n a l y s e i n d i q u e q u e I ' i n c e r t it u d e a b s o l u e d e s m e s u r e sd u r a y o n n e m e n t e f f e c t u 6 e s p a r le s d i s p o s i t if s le s p l u s r ~ c e n t s e s t in f 6 r i e u r e ~ - 0 , 5 m W / c m 2 .A u c o u r s d ' u n e s ~ r ie d ' e x l ~ r i e n c e s l e s a u t e u r s o n t c o m p a r ~ l '~ c h e l le r a d i o m 6 t r i q u e d 6 fi n ie p a r l e s i n s t ru -m e n t s d u J P L i t l ' 6 c b e l l e p y r h ~ l i o m 6 t r i q u e i n t e r n a t i o n a l e ( I P S ) . l l s o n t o b s e r v 6 q u e l e s m e s u r e s d u J P L6 t a l e n t s u p ~ r i e u r e s d e 2 , 2 % i t r 6 c h e l l e I P S .L a c o n s t a n t e s o l a ir e e t l a d i s t r i b u t io n s p e c t r a l e o n t 6 t 6 o b t e n u e s ~ p a r t ir d e m e s u r e s f a i t e s e n b a l l o n e nh a u t e a l t it u d e p a r 2 t y p e s d e r a d i o m ~ t r e s J P L it c a v i t6 . D e s m e s u r e s e f f e ct u 6 e s e n 1 9 6 8 it 2 5 k m d ' a l t i tu d eo n t d o n n 6 u n e v a l e u r d e l a c o n s t a n t e s o l a ir e d e 1 3 % 0 m W / c m 2. E n 1 9 6 9 d e s m e s u r e s f a i t e s it 36 k m o n td o n n 6 u n e v a l e u r d e 1 3 6 ,6 m W / c m z a v e c u n e i n c e r t it u d e a b s o l u e d e - - -0 , 5% . L e s r e n s e i g n e m e n t s s u r l es p e c t r e s o i a i r e o b t e n u s it p a r t i r d e c e s e x p e r i e n c e s s e r a p p r o c h e n t l e p lu s d u m o d u l e d u s p e c t r e s o l a i r e d eL a b s e t N e c k e l .R e s u m e n - U n a s e r ie d e r a d i 6 m e t r o s d e c a v id a d , d e v a l o r a b s o l u t o , d e s t i n a d o s a m e d i r ia ir r a d i a n c ia s o l a r,h a s i d o p u e s t a a p u n t o p o r e l J e t P r o p u l s i o n L a b o r a t o r y ( J P L ) . L o s a n f i li si s i n d i c a n q u e i a i n c e r t i d u m b r ea b s o l u t a d e l a s m e d i d a s d e i r r a d ia n c i a e f e c tu a d a s p o r l o s d i s p o s i t iv o s m i l s r e c i e n t e s e s m e n o s d e - + 0 , 5 r o W /c m 2 .

D u r a n t e u n a s e r i e d e e x p e r i m e n t o s , l a e s c a l a r a d io m ~ t r i c a d e f i n id a p o t l a i n s t r u m e n t a c i 6 n J P L h a s i d oc o m p a r a d a c o n i a E s c a l a P i r h e l io m ~ t r i c a l n t e r n a c i o n a l ( 1 P S ), o b s e r v ~ n d o s e u n a d i f e r e n c i a s is t e m / tt ic a d e l2 , 2 % c o n p r o d u c c i 6 n d e m e d i d a s s i s t e m ~ t i c a m e n t e m ~ is b a j a s p o r l a I P S .L a c o n s t a n t e s o l a r y l a d i s tr i b u c i 6 n e s p e c t r a l h a n s i d o e s t a b le c i d a s a p a r t i r d e m e d i d a s e f e c t u a d o sm e d i a n t e g l o b o s e n v u e l o s d e g r a n a l ti t u d c o n d o s m o d a l i d a d e s d e r a d i 6 m e t r o d e c a v i d a d J P L . L a s m e d i d a st o m a d a s a 2 5 k m e n e l a ~ o 1 9 6 8 p r o d u j e r o n u n v a l o r d e c o n s t a n t e s o l a r d e 1 3 7 , 0 m W / c m 2. D e i a s m e d i d a st o m a d a s e n 1 9 6 9 a 3 6 k m s e d e r i v 6 u n v a l o r d e 1 3 6 ,6 m W / c m 2 , e s t i m ~ n d o s e u n a i n c e n i d u m b r e a b s o l u t a d e-+ 0 , 5 % . L a i n f o r m a c i 6 n s o b r e e l e s p e c t r o s o l a r r e s u l t a n t e d e e s t o s e x p e r i m e n t o s c o n c u e r d a m ~ s a p r o x i m a d a -m e n t e c o n e l m o d e l o d e e s p e c t r o s o l a r d e L a b s y N e c k e l .I N T R O D U C T I O N - T H E A C T I V E C A V I T Y R A D I O M E T E R S

A S E R IE S o f c a v i t y r a d i o m e t e r s h a s b e e n d e v e l o p e d a t t h e J e t P r o p u l s i o n L a b o r a t o r yf o r t h e a c c u r a t e m e a s u r e m e n t o f s o l a r i r r a d i a n c e i n a b s o l u t e u n i t s [ 1 - 7 ] . A g r o u p o fi n s t r u m e n t s , f u n c t i o n a l l y d e s c r i b e d a s A c t i v e C a v i t y R a d i o m e t e r s , h a s e v o l v e d f r o m

* T h i s p a p e r p r e s e n t s t h e r e s u l t s o f o n e p h a s e o f r e s e a r c h c a r r i e d o u t a t th e J e t P r o p u l s i o n L a b o r a t o r y ,C a l i f o r n ia I n s t i tu t e o f T e c h n o l o g y , u n d e r C o n t r a c t N o . N A S 7 - 1 0 0 , s p o n s o r e d b y t h e N a t i o n a l A e r o n a u t i c sa n d S p a c e A d m i n i s t r a t i o n .t J e t P r o p u l s i o n L a b o r a t o r y , C a l i b o r n i a I n s t i t u te o f T e c h n o l o g y , P a s a d e n a , C a l i f o r n i a . U . S . A .2O3


2/9

2 0 4 R . C . W I L l _ S O Nt he S A C R A D [ 4 ] a n d P A C R A D [ 6 ] r a d i o m e te r s d e v el o p e d b y J . K e n d al l a t J P L .T h e s e d e v i c e s a r e d e s i g n e d f o r a u t o m a t i c , r e m o t e o p e r a t i o n i n a n y e n v i r o n m e n t a n dh a v e g r e a t p o t e n t ia l u s e f u l n e s s in a s tr o p h y s i c a l a n d m e t e o r o l o g i c a l s o l a r ra d i a ti o nm e a s u r e m e n t p r o g ra m s . T h e A c t i v e C a v i t y R a d i o m e t e r (o r A C R ) i s a s ta n d a r d d e t e c -t o r o f o p t i c a l r a d i a n t f l ux . I t d e f i n e s t h e a b s o l u t e r a d i a t i o n s c a l e t h r o u g h r e f e r e n c e t o a na c c u r a t e k n o w l e d g e o f i n s t ru m e n t a l , o p t i c a l, m e c h a n i c a l , a n d e l e c t r ic a l p a r a m e t e r s ,w i t h a n u n c e r t a i n t y o f l e s s t h a n - + 0 . 5 m W /c m '- '.

T h e e s s e n t ia l p h y s i c a l f e a t u r e s o f t h e A C R a r e s h o w n i n F ig . 1 . T h e A C R ' s c o n i c a lc a v i t y d e t e c t o r i s c o n n e c t e d b y a l o w th e r m a l i m p e d a n c e t o a h e a t s in k . T h e h e a t s in kis i n s u la t e d f r o m t h e e x t e r n a l e n v i r o n m e n t t o m i n i m i z e t h e r a te o f c h a n g e o f i ts te m -p e r a t u r e w h e n s u b j e c t e d t o fl u c tu a t in g t h e r m a l e n v i r o n m e n t s .

E X ~R N ~ VIEW L I M I ~ R - ~

I S01HERMAL IVIEW LIMITER | _,~~ A C N E S l U M ) ~ " ~HEATSINK5MAGNESIUM)~

CAVITY DETECTORCAVITYHEATER

BASE

i

I wte l

~ /2 . 5 "

/SUPPORT NYLON)

~ " ~ APERTURE~ x x

PLATINUMSENSORS/

~ S U P P O R T (N Y L O N )f CONNECTOR

b.'qb. 'q . . . . . . . . .EU~CmONICS

F i g. 1 . J P L a c t i v e c a v i t y r a d i o m e t e r T y p e 1 11 .

T h e i n t e ri o r s u r f a c e o f th e c o n i c a l c a v it y d e t e c t o r i s c o a t e d w i t h a s u r fa c e m a t e r i a lw h o s e e f f e c t i v e a b s o r p t a n c e f o r s o l a r r a d i a n t f l u x i s h i gh ( as = 0 . 9 5 _ 0 - 0 2) . T h e c a v i t y ' s2 c m d i a m . b a s e i s p a r ti a ll y s h a d e d b y a r o u n d a p e r t u r e t h a t b o t h d e f i n e s t h e d e t e c t o ra r e a f o r t h e r a d i o m e t e r a n d e n h a n c e s t h e e f f e c ti v e c a v i t y a b s o r p t a n c e . T h e a p e r t u r ec a n b e s h a p e d p r e c i s e l y a n d i ts s iz e d e t e r m i n e d w i t h g r e a t a c c u r a c y . T h e c a v i t y a b s o r p -t a n c e h a s b e e n a n a l y t i c a l l y s h o w n t o b e 0. 99 6- 4- 0- 00 2, e f f e c t i n g a 1 0 - f o ld d e c r e a s e i nt h e u n c e r t a i n t y o f t h e c a v i t y s u r f a c e a b s o r p t a n c y [8 ]. T h e f ie ld o f v ie w f o r t h e c a v i t yi s i s o t h e r m a l l y c o n f i n e d t o 2 0 b y t h e h e a t s i n k o r t o 5 w i t h t h e a d d i t i o n o f a n e x t e r n a lv i e w l im i t e r .T h e d i s s i p a ti o n o f a f ix e d a m o u n t o f p o w e r i n t h e c a v i t y w i ll p r o d u c e a c o n s t a n tt e m p e r a t u r e d r o p a c r o s s t h e t h e rm a l i m p e d a n c e . T h i s d r o p , t r a n s d u c e d b y p la t in u mw i n d i n gs , c a n b e c a l ib r a t e d a s a d i r e c t m e a s u r e o f th e i r r a d ia n t p o w e r o r u s e d t o a c t i v e l yc o n t r o l a n e l e c t ro n i c s e r v o s y s t e m a s in t h e A c t i v e C a v i t y R a d i o m e t e r . C i r c u i t r yh o u s e d i n t h e b a s e o f t h e r a d i o m e t e r a u t o m a t i c a l l y m a i n t a i n s c o n s t a n t c a v i t y p o w e rd i s s i p a t i o n b y co n t r o l l i n g a d . c . v o l t a g e s u p p l i e d t o a f i x e d - r e s i s t a n c e h e a t e r o n t h ec a v i t y . A s c h e m a t i c d r a w i n g o f t h is c i r c u i t i s s h o w n i n F i g. 2 .


3/9

New radlometric echniques 205

Where:

A C I I C U I C U I TIRIDGI: o +30 V tgO mA I

Standard detectorfunctionH = K(P c - Po)

H = Measured rradiance n absolute unitsPc = Cavityheater power with shutterclosedP0 = Cavityheater power with shutteropenK = (o~Ac) t = Standarddetectorconstant n terms of the instrumentalparameters

Fig. 2. ActiveCavity Radiometersystem.The ACR operates in a differential mode. The radiant source is chopped at low

frequency and the cavity heating power monitored in each phase. The irradiance isthen determined from these two electrical power measurements, along with the instru-mental constant which is the reciprocal of the cavity area-absorptance product.

The Active Cavity Radiometer has been shown theoretically to be capable of meas-uring solar irradiance with an absolute uncerta inty of less than - 0.5 mW/cm2 [5]. Itsgreatest single advantage, relative to radiometers employing flat detectors, is theshaded conical cavity detector, which reduces the uncertainty of the detector surfaceabsorptance by a factor of 10 [8].COMPARISON OF THE ABSOLUTE RADIOMETRIC SCALE, AS DEFINED BY THEACTIVE CAVITY RADIOMETERS, AND THE INTERNATIONALPYRHELIOMETRIC SCALE

A series of radiometer comparison tests was carried out at the JP L Table MountainObservatory during the period May 1968 to August 1970. Solar irradiance measure-ments by instruments reproducing the International Pyrheliometric Scale have beencompared with measurements made simultaneously by a number of different JPLActive Cavity Radiometers and PA CR AD radiometers.The results of these tests demonstrate a systematic difference between the ACRand PACRAD measurements and the IPS, with ACR irradiance measurementsexceeding those of the IPS by an average of 2.2 ___0.09 per cent. The average PA CR ADresults, reported elsewhere[7], have always demonstrated agreement with the ACRresults to well within the _+ 0.5 mW/cmz absolute uncertainty of the ACR. A summaryof the Table Mounta in Tes t results is included as Table 1.

Radiometer field of view can be an important factor in solar irradiance observationsmade through a substantial fraction of the earth's atmosphere. In the presence of largeoptical thicknesses of atmosphere aerosols, strong forward scattering (the solar aureoleeffect) can produce substantially different apparent irradiances for instruments withdifferent fields of view. Ancillary experiments performed during each Table Mountaintest have shown the turbidity parameter, as defined by Angstrom and Rhode[9], tobe less than 0.05. This defines, qualitatively, a relatively small aerosol optical thick-


4/9

2 0 6 R . C . W I L L S O NT a b l e ! . l n t e r c o m p a r i s o n o f J P L A c t i v e C a v i t y R a d i o m e t e r s a n d I n t e r n a t i o n a l P y r h e li o m e t r i c S c a l e. T e s tS it e: T a b l e M o u n t a i n O b s e r v a t o r y - L o c a t e d 6 0 m i le s S . E . o f P a s a d e n a , C a l if o r n ia in th e A n g e l e s N a t i o n a lF o r e s t a t 2 . 2 5 k m e l e v a t i o n

A v e r a g e v a l u e o f S t a n d a r d d e v i a t i o n A b s o l u t e u n c e r t a i n t yT e s t d a t e s c a l e d i f f e r e n c e o f s c a l e d i f f e r e n c e o f s c a l e d i f f e r e n c e

( m o / d a y / y r ) ( % ) + - ( % ) -+ ( % ) W e i g h t5 / 1 0 / 6 8 2"0 0' 135 / 1 1 / 6 8 2 ' 4 0 ' 0 99 /2 3 /68 2 ' 1 0" 079 / 2 4 / 6 8 2 " 3 0 ' 0 69 /2 5 /68 2" I 0 .044 / 2 3 / 6 9 2 " 4 0 ' 1 99 / 2 2 / 6 9 2 -3 0 ' 2 19 / 2 3 / 6 9 2 "3 0 " 058 /2 5 /7 0 2" I 0" 25

< 0"5 633162054318W e i g h t e dav er ag es 2-22 -4- 0 .09 - 0 .5

ness. Under these conditions, these authors conclude that an equivalent circular field-of-view for the Angstrom is 50-6 The effective difference between the Angstrom field-of-view and the 5 circular A CR field of view is therefore small. It does not appear tobe capable of producing a significant fraction of the 2.2 per cent scale difference.

The absolute uncertainty of irradiance measurements made by the Active CavityRadiometer under the Table Mountain Test conditions has been shown to be less than0.5 mW/cm2[10]. The nominal irradiance level at Table Mountain Test Site is 100mW/cm2, indicating that the International Pyrheliometric Scale contains a systematic,absolute error o f - 2.2 0. 5 per cent.

A recent confirmation of this result was obtained in an international comparisontest at Davos, Switzerland during September, 1970111]. Comparisons between theJPL PA CR AD radiometer[6, 7] and standard Angstrom Pyrheliometers used to definethe IPS yielded a- 1.8 per cent scale difference, in close agreement in magnitude andin the same direction as the Table Mountain results.

T H E S O I . A R C O N S T A N T D E R I V E D F R O M A C R B A L L O O N F L I G H TM E A S U R E M E N T S O F S O L A R I R R A D I A N C EFour high altitude ACR solar irradiance measurements have been attempted using

high altitude balloons as experimental behicles. In August 1968 the first flight gathereddata from 6 to 25 km altitude. The second flight in August 1 9 6 9 acquired useful databetween 25 and 36 km . Two succeeding attempts in 1969 and 1970 were frustrated byballoon failure during launch.

Data gathered during the two successful flights were obtained both with and with-out filters. Analysis of information content on atmospheric optics is currently in pro-gress. The solar constant results to be discussed here are derived from the solarirradiances measured at the maximum balloon altitudes.Solar constant values derived from the ACR balloon flight data contain three basiccorrections. The first is for the attenuation of solar irradiance by any window or filterincluded in the optical path. The second is for the attenuation of the remaining atmo-sphere above the ACR altitude. The third is for the Earth-Sun distance at the time of


5/9

New radiometric techniques 207m e a s u r e m e n t . C o m p u t a t i o n o f t h e s o l a r c o n s t a n t i s a c c o m p l i s h e d t h r o u g h t h e r el a ti o n -s h ip .

H o = H h R ~ [ T , o T A ] - ! ( 1 )w h e r e

/4 0 = s o l a r c o n s t a n tH h = s o l a r i r ra d i a n c e m e a s u r e d a t a lt i tu d e hR = E a r t h - S u n d i s t a n c e

T ~ = w i n d o w o r fi lt e r t r a n s m i t t a n c eTA = a t m o s p h e r i c t r a n s m i t t a n c e .

T h e a t m o s p h e r i c t r a n s m i t t a n c e i s d e t e r m i n e d f r o m t h e e q u a t i o n o f r a d i a t iv e tr a n s -f e r fo r p l a n e- p a r a ll e l a t m o s p h e r e s . T h e s o u r c e f u n c t i o n f o r t h e a t m o s p h e r e a b o v e t h eA C R i s a s s u m e d t o b e n e g l i g i b l e i n c o m p a r i s o n t o t h e d i r e c t s o l a r i r r a d i a n c e . T h ec o m p u t e d t o t a l ir r a d i an c e ( H D a t a l t it u d e h is/ ;h = H o ~ e x p - - [ rx s e c Z ] d k ( 2 )w h e r e

H % - - t h e e x t r a - a t m o s p h e r i c s o l a r s p e c t r a l i rr a d i a n c e~-~ = t h e a t m o s p h e r i c e x t i n c t i o n o p t i c a l t h i c k n e s sZ = t h e s o l a r z e n i t h a n g le .

T h e i n te g r al o v e r w a v e l e n g t h c a n b e a p p r o x i m a t e d t o t h e d e s i r e d a c c u r a c y b y as u m m a t i o n o v e r 3 7 d i s c r e te s p e c tr a l b a n d s . T h e b a n d s a r e c h o s e n t o a d e q u a t e l yd e s c r i b e t h e w a v e l e n g t h - d e p e n d e n t p r o p e r t i e s o f A C R w i n d o w s , fi lt e rs , a n d t h ea t m o s p h e r e . E q u a t i o n ( 2) t h e n b e c o m e s

37H h = Y~ H0.1 ex p - [Ti se c Z ] . (3)T h e e x t i n c t i o n o p t i c a l t h ic k n e s s i s d e t e r m i n e d f o r e a c h o f t h e 3 7 w a v e l e n g t h b a n d s .

T h e e x t i n c t i o n o p t i c a l t h i c k n e s s e s f o r R a y l e i g h a n d a e r o s o l s c a t te r i n g a n d f o r O z o n ea b s o r p t i o n a r e t a k e n f r o m E l t e r m a n n ' s t a b l e s [ 1 2]. E x t i n c t io n o p t i c a l t h i ck n e s s e s d u et o a b s o r p t i o n b y v i b r a t i o n - r o ta t i o n b a n d s o f t h e c o n s t a n t- m i x i n g - r a ti o a t m o s p h e r i cg a s e s 0 2 , C O s , C H 4 , a n d N 2 0 a r e d e r iv e d fr o m t h e re s u lt s o f H o u g h t o n e t a / . [ 1 3 ] .A b s o r p t i o n b y w a t e r v a p o r a n d o t h e r m i n o r a t m o s p h e r i c c o n s t i tu e n t s h a s b e e n f o u n dt o b e n e g l ig i bl e fo r a l t it u d e s a b o v e 2 5 k m . T h e e q u i v a l e n t w i d t h s a n d e x t in c t i o n o p t i ca lt h i c k n e s s e s f o r t h e s e g a s e s a r e s u m m a r i z e d i n T a b l e 2 . A t m o s p h e r i c p r o p e r t i e s f o r a llb a n d s a r e s h o w n i n T a b l e 3 .T h e w a v e l e n g t h d e p e n d e n t f e a t u r e s o f a t m o s p h e r i c , w i n d o w , a n d fi lt er t r an s -m i t t a n c e s p r o d u c e s a s e n s i t i v it y o f t h e d e r i v e d s o l a r c o n s t a n t t o t h e s p e c t r a l d i st ri -b u t i o n o f t h e e x t r a - a t m o s p h e r i c s o l a r i r r ad i a n c e m o d e l u s e d t o c o m p u t e t h e t w oq u a n t i t i e s : T ~ , t h e a t m o s p h e r i c t r a n s m i t t a n c e

T ~ = H J H o (4 )a n d T w , t h e t r a n s m i t t a n c e o f a w i n d o w o r f il te r,

37~, Tw.tHh. tt=1 ( 5 )

T w = H hS E V e L 1 4, N o . 2 - H


6/9

208 R . C . W I L L S O NTab le 2. Equivalent widths (W~) and ex tinction optical thickn esses (~-~)dueto constant-mixing-ratio, atmospheric gases

Wavelength Bandband Ga s center W3~.~ r~,~ W~.~(/zm) (t~m) (A) (A) Tzs.i0 " 7 5 - 0 " 7 7 0 2 0 ' 7 6 0 ' 2 2 0 " 00 1 1 I ' 0 0 " 00 5 01"4-1"5 CO z 1"4, 1"6 0"13 0"0010 0"5 0"00401" 9- 2 ' 1 C O 2 2 '0 0 '98 0" 0020 10 '0 0" 01702" 7- 2" 8 C O z 2 '7 36" 0 0 '037 0 270" 0 0" 31503 ' 2 - 3 " 5 C H 4 3 ' 3 3 " 0 0 ' 0 0 1 0 1 4 ' 0 0 " 00 5 04 " 1 7 5- 4" 4 25 C O z 4 ' 3 4 6 2" 0 0 " 20 4 0 1 6 6 3 " 0 1 " 0 9 4 04" 425- 5" 00 N z O 4 '5 3 '0 0" 0005 15 '0 0" 00305" 00- 100" 0 00 C O 2 15 '0 1573 '0 0" 0020 8990" 0 0" 0012

Gaseo us abundances: Ah = [ Mixing ratio x M T X P/Po]G as A2.~(27 mb) A3d6 mb) Ao(10 13 rob)

(atm-cm) (atm-cm) (atm-cm)02 4467.0 1191.0 167600.0CO2 6.67 1.78 300-0C H 4 0 .032 0 .0071 1 .2N 2 0 0 " 01 i 0 ' 0 0 2 3 0 " 4

F o u r s o la r s p e c tr u m m o d e l s th a t ar e p r o m in e n t in th e c u r r en t li 't er atur e h a v e b e e n u s e dt o c o m p u t e t h e s o l a r co n s t a n t . T h e s e a r e t h e m o d e l s o f A r v e s e n [ 1 4 ] , G a s t [ 1 5], L a b sa n d N e c ke l s [ 1 6 ], a n d T h e ka e ka r a [ 1 7 ]. T h e v a lu e s o f T A, T ~ ., H h , a n d H o w e r e c o m p u t e df o r e a c h m o d e l . T h e d e r i v e d H h ' s w e r e c o m p a r e d w i t h th e A C R m e a s u r e d i r ra d i an c e sa n d th e d i f f e r e n c e s u s e d a s in v e r s e s q u a r e w e ig h in g f a c to r s t o d e r iv e a f i f th a v e r a g es o l a r s p e c t ru m m o d e l . C o m p a r i s o n o f m e a s u r e d a n d c o m p u t e d H h ' s d e m o n s t r a t e dc l o s e s t a g r e e m e n t w i t h th e L a b s a n d N e c k e l m o d e l .

T h e a v e r a g e s p e c tr a l m o d e l w a s u s e d to c o m p u te th e fina l s o la r c o n s ta n t v a lu e sf o r th e th r e e A C R ' s in v o lv e d in th e 1 96 8 a n d 1 96 9 b a l l o o n f li g h ts . T h e s e r e s u l t s a n dth e ir u n c e r ta in t i e s a r e s u m m a r ize d in T a b le 4 . T h e la r g e s t s in g le s o u r c e o f e r r o r int h e 1 9 6 8 e x p e r i m e n t w a s t h e t ra n s m i tt a n c e o f t h e A C R q u a r tz w i n d o w . F o r t h e 1 9 6 9A C R i n s tr u m e n t , w h i c h h ad n o w i n d o w , t h e l a r g e st s o u r c e o f er r o r w a s t h e t e le m e t r yu n c e r ta in ty . T h e b e s t A C R s o la r c o n s ta n t v a lu e i s H 0 = 1 3 6"6 -+0 -7 m W /c m 2 d e r iv e dfrom the 1969 data .

C O M P A R I S O N O F T H E A C R A N D M U R C R A Y ' S I P S - R E F E R E N C E DB A L L O O N R A D I O M E T E RA s e r i e s o f h igh a l t itu d e s o la r i r r ad ia n c e m e a s u r e m e n ts h a v e b e e n m a d e b y M u r c r a y

e t a / . [1 8 ] o f th e U n i v e r s it y o f D e n v e r ' s D e n v e r R e s e a r c h I n s ti tu t e . U s i n g b a l l o o n -b o r n e r a d io m e te r s c a l ib r a te d o n th e I n te r n a t io n a l P yr h e l i o m e tr i c Sc a le , th e y d e r iv ea n a v e r a g e v a lu e f o r th e s o la r c o n s ta n t o f H 0 = 1 3 3.4 m W /c m 2.

A d i r ec t c o m p a r i s o n o f t h e U n i v e r s i t y o f D e n v e r r a d io m e t e r s a n d a n A C R w a sc a r r ie d o u t a t M t . E v a n s , C o lo r a d o , in Ju ly 1 97 0 . A s ys t e m a t i c d i f f e r e n c e o f 2 . 9 p e rc e n t w a s o b s e r v e d w i th A C R i rr a d ia n c e m e a s u r e m e n t s e x c e e d i n g t h o s e o f th e U n i v e r -s i ty o f D e n v e r r a d io m e te r s . I f th e r e s u l ts o f M u r c r a y a r e in c r e a s e d b y 2 . 9 p e r c e n t , a


7/9

New radiometric technique s 209

Table 3. Properties of earth' s atmosphere above 27 mb (- 25 kin) for weighted, average spectral modelSolar irrad. Solar

Spectral Extinction outside irradiance Attenuat ion ofbands optical atmosph ere at 25 km Atmosp heric irradiance

)kmi n hmaz thic kness H0,~ H 2 s . t tra nsmi tta nce (Ho,~ - His.i)(p.m) (p.m) ~i (mW/cm~) (mW/cm~) %s.~ (mW/cm~)0.000 0.275 25.4120 0.588 0.000 0.000 0 . 5 8 80-275 0.290 12.8440 0.373 0.000 0.000 0.3730.290 0.310 1.2510 1.069 0.238 0"223 0.8310"310 0.330 0.1320 1.515 1.293 0.854 0.2220.330 0.350 0.0260 1.844 1-788 0.969 0 .0570'350 0.370 0.0150 2'050 2.014 0 .9 52 0 .0370.370 0.390 0.0120 2.036 2.007 0 .9 86 0 - 0290-390 0"425 0.0090 5-398 5'340 0"959 0"0550"425 0'475 0.0060 9"561 9"493 0.993 0.0690"475 0-525 0.0080 9'632 9.540 0.990 0.0920"525 0.575 0'0140 9"392 9-236 0"983 O' 1560'575 0"630 0'0180 9.690 9.483 0-979 0 .2070"630 0.685 0.0090 8.605 8.513 0"959 0.0920'685 0"695 0.0040 1"470 1-463 0.995 0"0070"695 0"750 0.0020 7"482 7.464 0.998 0"0180.750 0-770 0-0040 2.500 2.488 0.995 0"0120.770 0"850 0.0000 8-916 8.916 1.000 0"0000"850 0"950 0.0000 9"035 9-035 1.000 0.0000"950 1'260 0'0000 18:564 18"564 , 1'000 0"0001"260 i"280 0"0000 0"894 0"894 1"000 0"0001"280 1'400 0"0000 5"112 5"112 1"000 0"0001'400 1"500 0'0040 0"954 0"950 0'995 0"0051.500 1-900 0'0010 10'496 10.484 0-999 0-0131.900 2.100 0.0170 0"758 0.743 0-980 0.0152' 100 2.500 0-0000 4.038 4.038 1.000 0.0002.500 2-670 0-0000 0'778 0.778 1.000 0"0002-670 2-700 0.0000 0" 126 O. 126 1.000 0.0002.700 2.800 0"3150 0"366 0.251 0"685 0.1152.800 2.850 0.0000 0-161 0.161 1-000 0.0002.850 3.000 0.0000 0.441 0.441 1.000 0-0003.000 3.200 0.0000 0"467 0'467 1-000 0.0003.200 3'500 0-0050 0"522 0-519 0-994 0-0033.500 3.800 0.0000 0"378 0.378 1.000 0.0003.800 4.175 0 .00~ 0"337 0"337 !-000 0-0004.175 4.425 1.0940 0.169 0'045 0-269 0"1244.425 5.000 0.0030 0.274 0"273 0"996 0"0015.000* * * * * * 0.0100 0"694 0"686 0'988 0.008

Table 4. S ummary of active cavity radiometer balloon-flight solar constant meas urem entsYE AR 1968 1968 1969

Radiometer ACR il No. 2 ACRI I No. 4 ACRI I No. 3Alti tude (km) 25 25 36Atmo sphe ric tran smit tanc e 0.9764_+0.0024 0.9766_+0.0024 0.9898_+0.0010Win dow trans mit tan ce 0.8945 -+ 0.0166 0.8990 _+ 0.0122 - -Ea rt h- Su n dis tance (AU) 1.01177_+25 10 -s 1.01177-+25 x 10-e 1.01396-+24 10-sSolar constant (mW/cm2) 136.6 +_ 2.8 137.3 _+ 2.2 136.6+_0.7


8/9

2 10 R . C . W I L L S O Ns o l a r c o n s t a n t v a l u e o f 1 3 7 .3 m W / c m 2 r e s u l ts , i n c l o s e a g r e e m e n t w i t h t h a t d e r i v e df ro m t h e A C R e x p e r i m e n t s ( S e e F ig . 3 ).

J P L A C R I I1 s o l a r c o n s t a n t = 1 36 .6 m W / c m 2D R I a v e r a g e s o l a r c o n s t a n t = 1 33 .4 m W / c m zA C R I I I / D R I c o m p a r i s o n r e su l t:

D = HA ca = 1'029-----0.0003HD.,A d j u s t m e n t o f H o oa i:

H gD a = i ' 02 9 X H oD al = 137" 3 m W /c m ~F ig . 3 . C o m p a r i s o n o f J e t P r o p u l s i o n L a b o r a t o r y A C R i l l w i t h D e n v e r R e s e a r c h I n s t i t u t eb a l l o o n r a d i o m e t e r s .

S U M M A R Y A N D C O N C L U S I O N ST h e J P L A c t i v e C a v i t y R a d i o m e t e r , a st a n d a r d d e t e c t o r o f o p t ic a l r a d ia n t f lu x ,c a n d e f i n e t h e a b s o l u t e r a d i a ti o n s c a l e w i t h a n u n c e r t a i n t y o f l e ss t h a n -- -0 . 5 m W / cm " .

D i r e c t c o m p a r i s o n o f t h e I n t e r n a ti o n a l P y r h e l i o m e t r i c S c a l e a n d s e v er a l A C R ' s h a sd e m o n s t r a t e d a s y s t e m a t i c d i f f e r en c e o f 2 . 2 p e r c e n t w i t h a s ta n d a r d d e v i a t i o n o f l e s st h a n _ 0 . l p e r c e n t a n d a n a b s o l u t e u n c e r t a i n t y o f l e s s t h a n _ 0 . 5 p e r c e n t . T h e I P S , a sp r e s e n t l y d e f in e d , a p p e a r s t o c o n t a i n a n a b s o l u t e e r r o r o f - 2 . 2 -+ 0 . 5 p e r c e n t .

T h e b e s t v a l u e o f t h e s o l a r c o n s t a n t d e r i v e d f r o m A C R b a l l o o n f l ig h t d a t a i s H 0 =1 3 6 . 6 _+ 0 . 7 m W / c m 2. T h i s r e s u lt c o m p a r e s w i t h t h e 1 3 3 .4 m W / c m ' r e s u lt o f t h e U n i -v e r s i ty o f D e n v e r ' s I P S r e f e r e n c e d v a l u e , d e t e r m i n e d f r o m b a l l o o n e x p e r i m e n t ss i m i l a r t o t h e A C R f l i g h t s . T h e 2 . 9 p e r c e n t d i f f e r e n c e m e a s u r e d b e t w e e n t h e s e t w ob a l l o o n - b o r n e r a d i o m e t e r s r e c o n c i l e s t h e m e a s u r e m e n t s t o w i th i n t h e ir e r r o r b o u n d s .

R E F E R E N C E SI l l F . H a l e y , A r a p id r e s p o n s e b l a c k b o d y c a v i t y r a d i o m e t e r . JPL New Technol. Rep. 3 0 - 5 2 1 , J e t P r o -p u l s i o n L a b o r a t o r y , P a s a d e n a , C a l if . ( 1 96 4 ) .[ 2] J . A . P l a m o n d o n a n d J . M . K e n d a l l , A c a v i ty - t y p e , a b s o l u te t o t a l r a d i a t io n r a d i o m e t e r . Space ProgramsSummary 3 7 - 3 5 , V o l . I V , J e t P r o p u l s i o n L a b o r a t o r y , P a s a d e n a , C a l i f. ( 1 96 5 ) .[ 3] R . C . W i l ls o n , R a d i o m e t e r C o m p a r i s o n T e s t s . JPL Tech. Memo. 3 3 - 3 7 1 , J e t P r o p u l s i o n L a b o r a t o r y ,P a s a d e n a , C a l if . ( 1 9 6 7 ) .[ 4] J . M . K e n d a l l , T h e J P L s t a n d a r d t o t a l ra d i a t i o n a b s o l u t e r a d i o m e t e r . Tech. Rep. 3 2 - 1 2 6 3 , J e t P r o -p u l s i o n L a b o r a t o r y , P a s a d e n a , C a l if . (1 9 6 8 ) .[5 ] R . C . W i ll s o n , E x p e r i m e n t a l a n d t h e o r e t i c a l c o m p a r i s o n o f t h e J P L a c t i v e c a v i t y r a d io m e t r i c s c a l e a n d

t h e i n t e r n a t i o n a l P y r h e l i o m e t r i c S c a l e . Tech. Rep. 3 2 - 1 3 6 5 , J e t P r o p u l s i o n L a b o r a t o r y , P a s a d e n a ,C a l i f . (1969) .[ 6 ] J . M . K e n d a l l , P r i m a r y a b s o l u t e c a v i t y r a d i o m e t e r . Tech. Rep. 3 2 - 1 3 9 6 , J e t P r o p u l s i o n L a b o r a t o r y ,P a s a d e n a , C a l i f ( i 9 6 9 ) .[ 7] J . M . K e n d a l l a n d C . M . B e r d a h l , T w o b l a c k b o d y r a d i o m e t e r s o f h i g h a c c u r a c y . J. appl. Opt. 9, 1082( 1 9 7 0 ) .[ 8] C . L . S y d n o r , A n u m e r i c a l s tu d y o f c a v i t y r a d i o m e t e r e m i s s i v i t ie s . Tech. Rep. 3 2 - 1 4 6 3 , . l e t P r o p u l s i o nL a b o r a t o r y , P a s a d e n a , C a l if . (1 9 7 0 ) .[ 9] A . A n g s t r o m a n d B . R h o d e , P y r h e l i o m e t r i c m e a s u r e m e n t s w i t h s p e c ia l r e g a rd t o th e c i rc u m s o l a r sk yr a d i a t i o n . Tellus 18 , 25 (196 6) .[ 1 0 ] R . C . W i l l s o n , T h e a c t i v e c a v i t y r a d i o m e t r i c s c a l e , t h e I n t e r n a t i o n a l P y r h e l i o m e t r i c S c a l e , a n d t h es o l a r c o n s t a n t . J. geophys. Res. 7 6 , 4 3 2 5 , 1 9 7 I .[ I I ] J . M . K e n d a l l , p r i v a t e c o m m u n i c a t i o n .[ 1 2 ] L . E . H e r m a n n , Handbook of Geophysics andSpace Environments, C h a p . 7 , p p . 7 - 1 4 - 3 5 . M c M i l l a n ,L o n d o n ( 1 9 6 5 ).


9/9

N e w r a d i o m e t r i c t e c h n i q u e s 2 1 1[ 13 ] J . H o u g h t o n , T h e a b s o r p t i o n o f s o l a r i n fr a r e d r a d i a t io n b y t h e l o w e r s t r a to s p h e r e . Quart. J. R. Met.Soc. !19, 319 (1963) .[ 1 4 } J . A r v e s e n et al. , D e t e r m i n a t i o n o f e x t ra - t e r r e s t r i a l s o l a r s p e c t r a l i r r a d i an c e f r o m a r e s e a r c h a i r cr a f t.J. appL Opt. 8 , 2215 (1969) .[ I 5] P . R. Ga st , Handbook of Geophysics and Space Environments, C h a p . 1 6, p . 1 6 - I . M c M i l l a n . L o n d o n(1965).[ 16 ] D . L a b s a n d H . N e c k e l , T h e r a d i a t io n o f t h e so l a r p h o t o s p h e r e f r o m 2 0 0 0 A t o 1 0 0p .. Z. Astrophys.6 9 , 1-73 (1968) .[ 17 ] M . D . T h e k a e k a r a , R . K r u g e r a n d C . H . D u n c a n , S o l a r i r r a d i a n ce m e a s u r e m e n t s f r o m a r e s e a r cha i r c r a f t . J. appl. Opt. 8, 1713 (1969).[ 1 8] D . G . M u r c r a y , T . G . K y l e , J . J . K o s t e r s a n d P . R . G a s t , T h e m e a s u r e m e n t s o f t h e s o la r c o n s t a n t f r o mh i g h a l t it u d e b a ll o o n s . R e p o r t N o . A F C R L - 6 8 - 0 4 5 2 , U n i v e r s i t y o f D e n v e r , D e n v e r , C o l o r a d o ( 1 96 8) .

nuevas técnicas radiométricas y mediciones constantes solares

Documents