RECENT PROGRESS IN INFRARED AND MICROWAVE ATMOSPHERIC SOUNDING

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RECENT PROGRESS IN INFRARED AND MICROWAVE ATMOSPHERIC SOUNDING

J. Harries

To cite this version:

J. Harries. RECENT PROGRESS IN INFRARED AND MICROWAVE ATMOSPHERIC SOUND- ING. Journal de Physique Colloques, 1980, 41 (C3), pp.C3-329-C3-335. �10.1051/jphyscol:1980383�.

�jpa-00219902�

JOURNAL DE PHYSIQUE Colloque C3, supplkment au no 4 , Tome 41, avril 1980, page C3-329

RECENT PROGRESS I N INFRARED AND MICROWAVE ATPlOSPHERIC SOUNDING Harries, J.E. * ,

National P h y s i c a l Laboratory, Teddington, ?.liddlesex TPI11 OLW U K

1 INTRODUCTION r e s u l t s o b t a i n e d by t h i s community i n r e c e n t times

w i l l be reviewed below. ^! As i m p l i e d i n t h e t i t l e , t h e m o s e o f t h i s

paper i s t o provide a r e p o r t on r e c e n t p r o g r e s s i n

a t m o s ~ h e r i c s o e c t r o s c o ~ y - i n t h e i n f r a r e d and 3 RECENT RESULTS I N INFRARED SPECTROSCOPY microwave r e g i o n s , and a l s o by i m p l i c a t i o n t h e

i n t e r m e d i a t e s p e c t r a l range namely t h e f a r i n f r a r e d . We a r b i t r a r i l y d e f i n e t h e s e r e g i o n s i n terms o f wavelength a s 1 - 30 vm, 30 - 500 um and 500 um - 5 mm.

We s h a l l n o t a t t e m p t a review of t h e h i s t o r i c a l background t o t h e s u b j e c t ; nor s h a l l we g i v e d e t a i l s of t h e b a s i c methods used i n atmospheric spectroscopy and t h e i r advantages and d i s a d v a n t a g e s , s i n c e t h i s a s p e c t was d e a l t w i t h i n a r e c e n t p a p e r . ( 1 )

The a p p l i c a t i o n i f I R t e c h n i q u e s t o s t u d i e s of t h e E a r t h ' s atmosphere i s n o t r e c e n t , and con- s i d e r a b l e work has been done o v e r a number of y e a r s t o develop s ch methods. ( 2 ) A p p l i c a t i o n s o f s u b m i l l i m e t r e ( 3 ~ and microwave(4) methods, however, i s more r e c e n t , having been s t r o n g l y developed i n only t h e p a s t decade. A s we s h a l l s e e below each of t h e s e q u i t e d i s t i n c t s p e c t r a l r e g i o n s h a s t h e p o t e n t i a l t o make s i g n i f i c a n t c o n t r i b u t i o n s t o atmospheric s c i e n c e .

The paper w i l l b e o r g a n i s e d a s f o l l o w s : S e c t i o n 2 w i l l l i s t t h e t y p e s of i n s t r u m e n t and t e c h n i q u e used i n c u r r e n t r e s e a r c h . S e c t i o n s 3, 4 and 5 w i l l t h e n review some o f t h e most r e c e n t p r o g r e s s i n t h e i n f r a r e d , s u b m i l l i m e t r e and microwave r e g i o n s , r e s p e c t i v e l y . S e c t i o n 6 w i l l p r o v i d e some comments on l i k e l y f u t u r e

developments .

2 TECHNIQUES

A wide v a r i e t y of i n s t r u m e n t s and

t e c h n i q u e s i s a v a i l a b l e t o t h e modern atmospheric s p e c t r o s c o p i s t . A s h o r t review of a v a i l a b l e t e c h n i q u e s h a s been p r e s e n t e d elsewhere( l ) , and f o r p r e s e n t purposes we s h a l l merely summarise, by means of Table 1 , t h e t e c h n i q u e s c u r r e n t l y b e i n g used by s e v e r a l groups a c t i v e i n t h i s f i e l d . An e x p l a n a t i o n of t h e e n t r i e s may b e found i n t h e key a t t a c h e d t o t h e t a b l e . We should o n l y n o t e h e r e t h a t a wide v a r i e t y of methods, i n c l u d i n g g a s c o r r e l a t i o n s p e c t r o s c o p y , resonance

f l u o r e s e n c e spectroscopy, a b s o r p t i o n and emission s p e c t r o s c o p y , implemented through s e v e r a l

d i f f e r e n t t y p e s of i n s t r u m e n t s a r e now .in u s e . Bearing i n mind t h a t Table 1 i s almost c e r t a i n l y incomplete, t h e r e i s c l e a r l y a g r e a t d e a l o f a c t i v i t y i n atmospheric spectroscopy a t a number o f i n s t i t u t i o n s . Some of t h e more o u t s t a n d i n g

Very c o n s i d e r a b l e advances i n our under- s t a n d i n g of t h e d e t a i l s of t h e I R spectrum of t h e atmosphere have been made through t h e work of D G Murcray, A Goldman, J Williams and t h e i r co1league.s a t Denver U n i v e r s i t y . Perhaps t h e most famous and a p p e a l i n g r e s u l t was t h a t o b t a i n e d about a decade ago, when a balloon-borne g r a t i n g s p e c t r o m e t e r a s used i n s o l a r o c c u l t a t i o n c o n f i g u r a t i o n 7 5 ) t o make measurements o f t h e a b s o r p t i o n spectrum i n t h e 11 vm r e g i o n o v e r very l o n g o p t i c a l p a t h s . As i s i l l u s t r a t e d by F i g u r e 1 , a s measurements were made a t i n c r e a s i n g z e n i t h a n g l e s from about 8g0 t o 940, a q u i t e s t r o n g a b s o r p t i o n band ( t h e v5 and 2 9

v i b r a t i o n s ) due t o HNO3 was r e v e a l e d . The n i t r i c a c i d molecule had p r e v i o u s l y been i d e n t i f i e d a t d i f f e r e n t w a v i i p g t h s (vh band a t about 1300 em-,') by t h i s group b u t t h e r e s u l t a t 11pm provided a very c l e a r and convincing c o n f i r m a t i o n of t h e e x i s t e n c e of HN03, i n a l a y e r c e n t r e d a t about 25 km a l t i t u d e , I n t h e s t r a t o s p h e r e . The vg and 2vg bands have s i n c e been used e x t e n s i v e l y by a number of groups f o r remote measurements o f t h i s s t r a t o s p h e r i c c o n s t i t u e n t .

1 Measuremen_t~ o f s o l a r t r a n s m i s s i o n i n t h e 800-950 cm r e g l o n from a b a l l o o n f l o a t i n g a t approximately 30 km. Each t r a c e i s a

s e p a r a t e s p e c t r a l s c a n , o b t a i n e d a t t h e s o l a r z e n i t h a n g l e shown a g a i n s t i t , and t h e r e s u l t s a r e d i s p l a c e d by 20% f o r c l a r i t y . The growth o f a b s o r p t i o n f e a t u r e s due t o HNO ₃ a r e c l e a r l y observed. ( ~ r o m r e f . 5 )

60 - 40 -

* W r i t t e n i n p a r t w h i l e t h e a u t h o r was on l e a v e of absence a t t h e Eat i o n a l Cknter f o r AtmospPeric Research, Boulder, Colorado, USA.

20 - 0 .

800 850 900 950

WAVENUMBER (cm-']

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980383

C3-330 ^{JOURNAL DE PHYSIQUE}

Another example of t h e very c l e a r and methodical work which has been done by t h e Denver group i n o r d e r t o c l a r i f y t h e d e t a i l s o f t h e I R spectrum i s shown i n Figure 2. This example a l s o i l l u s t r a t e s t h e importance o f a thorough species- by-species consideration of a complex atmospheric spectrum when t r y i n g t o a s s i g n f e a t u r e s observed i n t h a t spectrum; t h e most convincing way of achieving a f i r m s e t of assignments i s t o b u i l d up an exact simulation o f t h e observed splctrum, using e i t h e r measured l a b o r a t o r y s p e c t r a f o r t h e d i f f e r e n t gases involved, o r computer simulation of t h e i r s p e c t r a using t h e o r e t i c a l models o f t h e molecular absorption processes. Figure 2 shows a s o l a r transmission spectrum i n t h e 1602-1618 cm-I region (frame 1 ) obtained from an a i r c r a f t f l y i n g a t

-

(4) NO2 ONLY

1

1604 1606 1608 I610 1612 1614 1616 WAVENUMBER (cm-'1

2 Measurements o f s o l a r transmission i n t h e 1610 em-' region from an a i r e r a 3 a t about 15km a l t i t u d e ( ~ r a m e I ) , compared with a c a l c u l a t e d spectrum (Frame 2 ) which i s produced from t h e i n d i y i d u a l s p e c t r a shown i n Frames 3 - 5.

(From Ref. 2 1 _, ) .

product of 3, 4 and 5. The c l o s e s i m i l a r i t y between t h e t o p two frames c l e a r l y shows t h a t NO2 absorption f e a t u r e s have been d e t e c t e d (eg a t 1604,5'cm-', 1606 em-' and 1611.5 em-'), and a l s o t h a t all t h e major f e a t u r e s of t h i s s p e c t r a l region a r e w e l l understood. Some d e t a i l s remain t o be c l a r i f i e d though ( c f t h e small f e a t u e s a t

1613.0 - 1633.5 cm-I), and one s u s p e c t s t h a t remaining u n c e r t a i n t i e s may w e l l r e s i d e i n imperfect s p e c t r a l l i n e d a t a .

Extensive measurements of t h e I R absorption spectrum have a l s o been made f o r

s e v e r a l y e a r s by t h e group a t t h e J e t Propulsion Laboratory under C B Farmer. The technique used by t h i s group i s high speed (of scanning) Fourier transform spectroscopy u s i n g a Michelson

WAMNUMBER, cm-'

3 Atmospheric transmission o f s o l a r r a d i a t i o n measured along a limb path a t an a l t i t u d e of about 35 km u s i n g a Michelson i n t e r f o r o m e t e r i n t h e 2900 and 4000 cm-I regions. Absorption f e a t u r e s due t o s t r a t o s p h e r i c HF and HC1, and s o l a r CO (8) a r e marked. (From Ref. 7 )

iriterferometer. An examplet7) of t h e work of t h i s group i s given i n Figure 3, which shows p o r t i o n s of atmospheric absorption s p e c t r a i n two s p e c t r a l r e g i o n s , around 2926 and 4038 cm-I, observed u s i n g s o l a r o c c u l t a t i o n methods from a balloon a t

-

(from which p r o f i l e s of t h e H C 1 and HF d i s t r i - butioqs were c a l c u l a t e d ) a s w e l l a s s 1 r CO.

(marked .@(. Others ( i n c l u d i n g ZanderP8T et oz and B u i j s 9 ) ) have a l s o made measurements a t t h e s e s h o r t I R wavelengths, using high r e s o l u t i o n g r a t i n g spectrometers o r Michelson i n t e r f e r o - meters mounted on balloons.

ALTITUDE 4 0 t m DISTANCE ZENITHALE e 07O

, ,cm-'

-

1915 1910 1905 1902

I Ll I I I I

POSITION DES RAILS DE NO TRANSMISSION O o P

ALTITUDE DE VDL 1 5 . 5 L n DISTANCE ZENITHALE 9 I 0 3 O '

V

13.7.73 MATIN Ii20

1 8 8 9 . 5 8 0 TRANSMISSION 0.9

4 Measurements of t h e s t r a t o s p h e r i c s o l a r t r a n s - mission spectrum u s i n g a G r i l l e spectrometer

from a b a l l o o n ( t o p c u r v e ) and an a i r c r a f t (bottom c u r v e ) , f o r measurements of NO.

Measurement c o n d i t i o n s given on t h e diagram and i n t h e t e x t . ( ~ r o m Ref 1 2 ) .

5 Aircraft-borne G r i l l e s p e c t r o m e t e r measurements made over a wide range o f l a t i t u d e s have been a n a l y s e d t o g i v e t h e NO, NO2 and HNO

c o n c e n t r a t i o n s p l o t t e d h e r e ( i n t o t a ? column d e n s i t y u n i t s , above t h e o b s e r v e r ) . (From Ref. 13)

I n Europe, h i g h r e s o l u t i o n I R spectroscopy h a s been s t u d i e d i n d e t a i l by t h e groups under G i r a r d i n France and Ackerman i n Belgium, oyten working t o g e t h e r ( l o ) . Measurements made by t h i s group have u t i l i s e d t h e ingenious G r i l l e s p e c t r o - m e t e r ( 11 ) which o p e r a t e s e s s e n t i a l l y a s a g r a t i n g s p e c t r o m e t e r but u t i l i s e s compound e n t r a n c e and e x i t s l ' t s t o improve energy throughput. A s an examplet12) o f t h e s e groups' work, Figure 4 p r e s e n t s (upper c u r v e ) t h e atmospheric a b s c r p t i o n spectrum measured from a b a l l o o n a t an a l t i t . d e o f 40 km on May 14 1973 d u r i n g s u n r i s e , showing f e a t u r e s due t o H20, C02 and NO i n t h e 1910 cm-I r e g i o n ; t h e lower curve shows a r e s u l t i n t h e

1890 cm-1 range t a k e n l o o k i n g a t t h e sun d u r i n g s u n r i s e from an a i r c r a f t f l y i n g a t 15.5 km w i t h a s o l a r z e n i t h a n g l e of 91.5' on J u l y 13 1973, a g a i n showing H20, C02 and N O l i n e s .

Recently an e x t e n s i v e s e r i e s of measurements by t k e G i r a r d group have been made from an a i r - c r a f t d u r i n g t h e " m t i t u d e Survey P r o g r a m U ( l 3 ) . Data s i m i l a r t o t h a t shown i n F i g u r e 4 were r e c o r d e d a t an a l t i t u d e of about 11 km _from ~ O O N

t o 600 S , and t h e s p e c t r a were i n t e r p r e t e d t o y i e l d l a t i t u d i n a l c r o s s s e c t i o n s o f t h e t o t a l amount of a number of g a s e s above t h e f l i g h t l e v e l . Figure 5 shows such d a t a f o r N O , NO2 and HNo3( l 3 ) , t h r e e molecules i n t i m a t e l y concerned w i t h t h e s t r a t o s p h e r i c ozone balance. C l e a r l y a s t r o n g l a t i t u d i n a l dependence o f HNO3 i s s e e n , though t h e v a r i a t i o n of NO + NO2 i s r e l a t i v e l y weak.

The r e s u l t s d i s c u s s e d s o f a r have been o b t a i n e d u s i n g i n c o h e r e n t non-monochrom t

"c lt7

t e c h n i q u e s . A r e c e n t r e s u l t by Menzies ,

employing i n f r a r e d l a s e r heterodyne methods i s remarkable b o t h f o r t h e d a t a it produced a s much a s f o r t h e t e c h n i c a l advances it r e p r e s e n t e d . I n t h i s experiment a l a s e r heterodyne spectrometer ( l 5 ) o p e r a t i n g i n t h e 853 cm-'region was flown on a high a l t i t u d e b a l l o o n and used t o observe t h e sun a l o n g a limb p a t h . The a b s o r p t i o n s p e c t r a which were r e c o r d e d a s a f u n c t i o n of t h e b e a t frequency between t h e incoming r a d i a t i o n and t h e l a s e r l o c a l o s c i l l a t o r i s shown i n F i g u r e 6. The arrow marks t h e p o s i t i o n o f a l i n e due t o C10 a s measured e x p e r i m e n t a l l y : t h e observed a b s o r p t i o n has been i n t e r p r e t e d t o d e r i v e t h e v e r t i c a l d i s t r i b u t i o n of C10 which i s shown i n F i g u r e 7.

Also shown i n F i g u r e 7 a r e t h e r e s u l s f model c a l c u l a t i o n s o f t h e C10 d i ~ t r i b u t i o n ~ ~ 49.

One f u r t h e r a r e a which perhaps m e r i t s mention i s t h e development i n r e c e n t y e a r s o f c r y o g e n i c a l l y cooled s p e c t r o r a d i o m e t r i c d e v i c e s f o r I R atmospheric o b s e r v a t i o n s . Murcray and co-workers have r e p o r t e d t h e u s e o f a l i q u i d helium-cooled g r a t i n g s p e c t r o m e t e r ( 1 6 ) , and r e c e n t l y a l i q u i d nitrogen-cooled g r a t i n g s p e c t r o - meter developed by t h e NPL group h a s been flown on two o c c a s i o n s on a h i g h a l t i t u d e a 1 oon t o

?17?

c a r r y o u t limb-sounding o b s e r v a t i o n s . The n e c e s s i t y f o r c o o l i n g a s p e c t r o m e t e r comes, o f c o u r s e , from t h e d e s i r e t o reduce background and s t r a y r a d i a t i o n from and w i t h i n t h e s p e c t r o - meter t o a minimum s o a s t o o b t a i n h i g h e r r a d i o m e t r i c s e n s i t i v i t y t o weak atmospheric e m i s s i o n s . T e c h n i c a l l y , o f c o u r s e , t&s imposes q u i t e s e v e r e d i f f i c u l t i e s which have, however, been overcome. Measuremen s ' n t h e 8 - 15 pm

117)

r e g i o n u s i n g such a d e v i c e have allowed s i m u l t a n e i o u s o b s e r v a t i o n s o f t h e d i s t r i b u t i o n s o f H20, 0 3 , HNOg, CH4 and N20.

c3-332 JOURNAL DE PHYSIQUE

4 RECENT RESULTS I N SUBMILLIMETRE SPECTROSCOPY

A t s u b m i l l i m e t r e o r f a r i n f r a r e d wave- l e n g t h s , t h e s i t u a t i o n u t o about 1976 h a s r e c e n t l y been A t t h e s e l o n g i n f r a r e d wavelengths t h e atmospheric spectrum i s made up p r i m a r i l y of o v e r l a p p i n g pure r o t a t i o n s p e c t r a of d i g o l a r atmospheric molecules. Because o f t h i s high degree of o v e r l a p , high s p e c t r a l r e s o l u t i o n i s e s s e n t i a l and p r o g r e s s has been d e f i n e d l a r g e l y by t e c h n i c a l developments which have y i e l d e d t h e p o s s i b i l i t y of i n c r e a s e s i n r e s o l u t i o n . S i n c e t h e review given i n r e f e r e n c e 3, t h e most

s i g n i f i c a n t p r o g r e s s h a s o c c u r r e d through t h e work of two groups.

The f i r s t i s t h a t a t t h e U n i v e r s i t y of Calgary, which h a s flown a rapid-scan f a r i n f r a r e d Michelson i n t e r f e r o m e t e r on b a l l o o n f l i g h t s , - l producing s p e c t r a a t a r e s o l u t i o n of 0.05 cm .

These ne d t a , an example o f which i s shown i n F i g u r e 8 7 1 ~ 7 , have allowd t h e t e n t a t i v e i d e n t i f i - c a t i o n o f OH and o t h e r s p e c t r a l f e a t m ' e s i n t h e very f a r i n f r a r e d , f o r t h e f i r s t time.

The second i s t h a t a t t h e I n s t i t u t e f o r Research on Electromagnetic Waves, i n F l o r e n c e , I t a l y , which i n a c o l l a b o r a t i v e experiment w i t h t h e NPL h a s r e c e n t l y flown a very high r e s o l u t i o n Micelson (0.004 cm-l) on a b a l l o o n : s p e c t r a l d a t a a r e s t i l l b e i n g transformed from t h e i n t e r f e r o - grams o t a ned by t h i s experiment, but f i r s t r e s u l t s y 1 9 f appear t o confirm t h a t t h e f u l l r e s o l u t i o n has been achieved, and t h a t e x c e l l e n t q u a l i t y s p e c t r a should f o l l o w s h o r t l y .

TANGENT HE IGHIS :

SUN--\

I I

1700 1800 ^C

BEAT FREQUENCY. MHz

6 S o l a r t r a n s m i s s i o n s p e c t r a a s measured a t a number o f t a n g e n t h e i g h t s from a b a l l o o n u s i n g a l a s e r heterodyne s p e c t r o m e t e r . The arrow marks t h e (measured) p o s i t i o n o f a C10 l i n e a t 853.18104 cm-I. ( ~ r o m Ref. 14)

As an example of t h e n a t u r e o f t h e r e s u l t s which a r e expected, we s h o w . i n F i g u r e 9 a spectrum - c a l c u l a t e d by t h e NPL g r o u p ( 2 0 ) , an

LIU, DONAHUf. C ICIRONLa4 1976

t-44-4

7 The C10 volume mixing r a t i o deduced from t h e d a t a of F i g u r e 6 , compared with c a l c u l a t i o n (From Refs. 14 and 2 2 ) .

8 Measurements of t h e f a r i n f r a r e d ( s u b m i l l i - metre) s t r a t o s p h e r i c emission spectrum ( t o p c u r v e ) , measured w i t h a Michelson i n t e r - f e r o m e t e r mounted on a b a l l o o n package a t about 33 km a l t i t u d e , and a t a z e n i t h a n g l e of 80' . The lower curve shows a c a l c u l a t e d spectrum i n c l u d i n g l i n e s of H20 and O3 o n l y . The p o s i t i o n s of l i n e s o f o t h e r s t r a t o s p h e r i c c o n s t i t u e n t s a r e shown. (From Ref 18)

emission spectrum i n t h e 40 cm-' r e g i o n f o r t h e c a s e of a b a l l o o n ( o r s a t e l l i t e ) e f f e c t i v e l y above t h e s t r a t o s p h e r e l o o k i n g towards t h e atmospheric limb a t a t a n g e n t h e i g h t of 30 km. The s o l i d curve shows t h e p r i n c i p a l f e a t u r e s of t h e spectrum, due t o H20, 02 and 03, and t h e d o t t e d curve shows t h e e f f e c t of adding H C 1 and HF a t a mixing r a t i o o f 10-9 by volume ( c o n s t a n t w i t h h e i ' h t ) . This c a l c u l a t i o n c l e a r l y i n d i c a t e s t h a t e t e n f o r mixing r a t i o s 10 t o 30 times s m a l l e r t h a n t h e v a l u e used, measureable l i n e s due t o H C 1 and HF should b e observable.

5 RECENT RESULTS I N MICROWAVE SPECTROSCOPY During t h e p a s t f i v e years o r s o t h e determination of upper atmosphere t r a c e gas composition using microwave methods has progressed considerably, p r i m a r i l y through t h e work oq Waters and co-workers. Systems have been

developed f o r ground-based and a i r c r a f t - b o r n e measurements o f H20, O3 and CO, based on t h e monxhromatic heterodyne methods p o s s i b l e a t frequencies below about 400 GHz. A review of microwave atmospheric spectroscopy has r e c e n t l y been presented by Waters. (4)

Figure 10 shows a general view of t h e atmospheric transmission spectrum from sea l e v e l , showing ( f o r a v e r t i c a l p a t h ) t h e components due t o 02, 0 3 and H20; 03 i s r e s p o n s i b l e f o r t h e many narrow l i n e s seen between 100 and 300 GHz i n t h e

diagram. A t t h e very high s p e c t r a l r e s o l u t i o n ( < 1 MHz) achievable a t t h e s e frequencies ( r e s o l v i n g powers of about 105 - l o 6 ) it i s p o s s i b l e t o r e s o l v e t h e "window" regions between t h e f i n e s t r u c t u r e due t o 03, where weak l i n e s

due t o o t h e r t r a c e c o n s t i t u e n t s such a s CO, N20, NO, NO2, H202 and o t h e r s , e x i s t t 4 ) .

As an example of t h e r e s u l t s which may now be obtained. Figure 11 shows a measurement o f t h e CO l i n e a t 1 15.271 GHz ( d o t s ) , and t h e r e s u l t s of c a l c u l a t i o n s of t h e p r e d i c t e d l i n e shape f o r t h r e e d i f f e r e n t assumed CO d i s t r i b u t i o n s , A, B and C.

These p r o f i l e s a r e shown i n Figure 12: t h e s p e c t r a l d a t a of Figure 11 c l e a r l y show t h a t p r o f i l e B provides t h e b e s t fit t o t h e measure- ments. This r e s u l t may perhaps i n d i c a t e t o t h e r e a d e r t h e high p r e c i s i o n f o r upper atmospheric measurements now p o s s i b l e using microwave systems.

HF = l ppb

HC1 = I p p b O3

1 1 1

41 4 2

c m - '

CALCULATED EM1 SSlON S?ECIX;)tA

9 A c a l c u l a t e d emission spectrum i n t h e 41 - 42 cm-1 region of t h e f a r i n f r a r e d , f o r , an observer o u t s i d e t h e atmosphere viewing t h e limb a t a tangent h e i g h t of 30 km. The

s p e c t r a l r e s o l u t i o n i s 0.01 cm-l. The calcula- t i o n included H20, 0 2 , f)3, HF and HC1, and t h e s i g n i f i c a n c e of t h e varlous s p e c t r a l f e a t u r e s i s discussed i n t h e t e x t . (From Ref. 20)

6 ,, , , , , , , , , ,

,

,

,

,I

50 100 150 200 250 3 0 0

FREOUENCY (GHz)

10 Calculated z e n i t h microwave absorption spectrum f o r s e a l e v e l c o n d i t i o n s . The s e p a r a t e c o n t r i b u t i o n s of H20, 02 and O3 a r e shown. (From Ref. 4 )

11 Measurements of a CO emission l i n e a t 115.27 MElz using a microwave spectrometer a t s e a l e v e l looking towards t h e z e n i t h . Curves A, B and ^C a r e computed l i n e shapes f o r t h e t h r e e CO d i s t r i b u t i o n s shown i n Figure 12. (From Ref. 23)

I 2 Three assumed CO p r o f i l e s used i n t h e c a l c u l a t i o n of s p e c t r a l l i n e shape shown i n ' Figure 1 1. (From Ref. 23)

6 THE FUTURE

It should be c l e a r from t h e examples c i t e d above t h a t t h e spectroscopic study of t h e upper atmosphere a t wavelengths between 1 urn and 1 mm

c3-334 JOURNAL DE PHYSIQUE

i s a very a c t i v e f i e l d . For t h e immediate f u t u r e one can s e e t h a t c e r t a i n s p e c i f i c a r e a s a r e almost c e r t a i n t o show r a p i d p r o g r e s s ; amongst t h e s e a r e a s we may include:-

.

Cryogenic s p e c t r o m e t e r s and i n t e r f e r o m e t e r s f o r high r a d i o m e t r i c s e n s i t i v i t y and p r e c i s i o n f o r measurements o f v e r y weak atmospheric emissions throughout t h e i n f r a r e d .

.

m.

Microwave heterodyne s p e c t r o s c o p y , a g a i n c a p a b l e of v e r y high r e s o l u t i o n and a l s o of r a p i d l y improving n o i s e l i m i t s a s components a r e improved and a s , f o r example, cooled mixers and d e t e c t o r s become a v a i l a b l e .

A s t h e v a r i e t y o f a v a i l a b l e i n s t r u m e n t s and t e c h n i q u e s i n c r e a s e s , it i s important t o remember t h a t d i f f e r e n t atmospheric i n v e s t i g a t i o n s demand d i f f e r e n t i n s t r u m e n t a l q u a l i t i e s , so t h a t it seems l i k e l y t h a t we w i l l c o n t i n u e t o r e q u i r e a

combination of measurements: it i s most u n l i k e l y t h a t any one t y p e w i l l p r o v i d e t h e panacea f o r a l l measurement r e q u i r e m e n t s .

A s a f i n a l p o i n t , we m u s t r e c o g n i s e t h e growing need t o develop s a t i s f a c t o r y remote s e n s i n g methods i n two o t h e r a r e a s o f g e o p h y s i c a l s e n s i n g . The f i r s t i s i n t h e remote d e t e r m i n a t i o n of upper a i r winds ; t o d a t e a number of h i g h r e s o l u t i o n methods have been proposed i n t h e v i s i b l e , i n f r a r e d and microwave r e g i o n s , each c a p a b l e of measuring

( w i t h l i m i t e d a c c u r a c y ) t h e Doppler s h i f t s caused by wind motions. This i s a d i f f i c u l t measurement problem, however, which s t i l l r e q u i r e s a s a t i s f a c - t o r y s o l u t i o n . The second concerns t h e remote s e n s i n g o f t h e t e m p e r a t u r e and s t a t e of t h e oceans, which a c t a s huge r e s e r v o i r s o f energy i n t h e atmosphere - ocean system, and which a r e b e l i e v e d t o p l a y a dominant r o l e i n c o n t r o l l i n g t h e E a r t h ' s c l i m a t e . Here a g a i n , d i f f i c u l t measurement problems exis: ( e g t h e e f f e c t o f c l o u d s , h a z e , molecular t r a n s m i s s i o n , waves, e t c ) which r e q u i r e d e t a i l e d s t u d y b e f o r e a r e l i a b l e remote s e n s i n g system can be evolved.

7 J.E. HARRIES, Phi1.Trans.Roy.Soc. ( I n p r e s s ) . 2 A. ADEL,'Chapter 10 o f "The Atmosphere o f

t h e E a r t h and P l a n e t s " , Ed. G. Kuiper, Chicago U n i v e r s i t y P r e s s , 1949.

5 D.G. MURCRAY, T.G. KYLE, F.H. MTJRCIIAY and W.J. WILLIAMS, ~.Opt.Soc.Am., 2, 1131, 1969-

6 D.G. MURCRAY , ^T .G. KYLE, F.H. WCRAY and W . J . WILLIAMS, Nature 218, 78, 1968.

7 C.B. FARMER and C.F. RAPER, Geophys. Res.

L e t t s , 1, 527, 1977.

8 R . TANDER, G. ROLAND and L. DELBOUILLE, Geophys. Res. L e t t s . , A, 117, 1977.

9 H.L. BUIJS, G. VAIL and G. TREMBLAY, P r i v a t e communication, 1977

10 M. ACKERMAN, D . FRIMOUT, C. m L E R ,

D. NEVEJANS, J - ^C FONTANELLA, A. GIRARD and N . LOUISNARD, Nature 2&, 205, 1973.

11 A. GIRARD, Appl.Optics, 2, 79, 1963.

12 A. GIRARD, Acta A s t r o n a n t i c a , 1, 237, 1974.

13 A. GIRARD, J . BESSON, R . GIRAUDET and L. GRAMONT, Pageoph., 117, 381, 1978/79.

14 R.T. MENZIES, Geophys. Res. L e t t s . , 6, ^151,

1979.

15 R.T. MENZIES, Opt .Eng., IJ44, 1978.. , 16 W . J . WILLIAMS, D.B. BARKER, J . N . BROOKS,

A. GOLDMAN, J.J. KOSTERS, F.H. MURCRAY, D.G. MURCRAY and D.E. SNIDER, Proc.Soc.

Photo-Optical I n s t r . Engineers, San Diego, C a l . , Aug. 1976.

17 S. POLLITT, R.H. BRADSELL, J . E . HARRIES, D.G. MOSS and N.R. SWANN. To b e p u b l i s h e d . 18 D.J.W. KENDALL and T.A. CLARK, I n f r a r e d Phys.,

18, 803, 1978.

-

19 B. CARLI, F.MENCARAGLIA and A. BONETTI, P r i v a t e communication, 1979.

20 M . J . BANGIiAM, I n f r a r e d Phys. l8, 357, 1978.

21 D.G. MURCRAY, A. GOLDMAN, W . J . WILLIAMS, F.H. MURCRAY, J . N . BROOKS, J Van ALLEN, R.N. STOCKER, J.J. KOSTERS and D.B. BARKER, Proc. 3 r d Conference on CIAP, US. Dept of T r a n s p o r t a t i o n , 1974.

22 S. LIU, R . J . CICERONE and T.M. DONAHUE, Proc.Int.Conf. on Problems r e l a t e d t o t h e S t r a t o s p h e r e , Logan, Utah, 1976.

23 J . W . WATERS, W . J . WILSON and

F . I . SHIMABUKURO, S c i e n c e , a, 1174, 1976.

3 J.E. HARRIES, J.Opt .Soc .Am., 2 7 , 880, 1977.

4 J .W. WATERS, Chapter 2 o f "Methods o f Experi- mental Physics" Vol 12B, Ed. M.L. Mceks, Academic P r e s s , 1976.

TABLE 1

Atmospheric Spectroscopy: A Selection of Groups/Techniques

Key to Table 1 IR Infrared W Ultra-violet

Solar Occ solar occultation FIR Far infrq-ed

GS grating spectrometer SCR Selectix -hopper radiometer MI Michelson interferometer PMR Pressure modulator radiometer GROUP

Ackerman/Girard et al.

Andersonet al.

Buijs et al.

Clark & Kendall Evans et al.

Farmer et al.

Gille et al.

Harries et al.

Heath/Kreuger Houghton et al.

Menzies et al.

Murcray et al.

Pate1

Offerman et al.

Stair et al.

Waters Zander

COUNTRY France USA Canada Canada Canada USA USA UK

USA UK USA USA USA West German USA USA Belgium

TECHNIQUE

Grille spectrometer/IR solar occ .

Resonance Fluorescence/local measurement MI/solar Occ

FIR MI/atmos . ^emission

GS/MI/W and IR solar occ. and atmos. emission MI/solar occ.

Filter radiometer/atmos. emission FIR MI/Cryogenic GS/atmos. emission

W Spectrometer/solar trans and backscatter SCR/PMR/atmos emission

IR laser heterodyne/solar occ.

GS (cooled and uncooled)/solar occ/atmos emission Laser absorption using Spin-Flip Raman Laser/

local measurement

Cryogenic GS/atmos. emission GS/Cryogenic MI/atmos emission Microwave spectrometer/atmos emission GS/solar occ

PLATFORM

Balloon, aircraft Balloon, rocket Balloon

Balloon

Balloon, rocket Balloon, aircraft Balloon, satell-ite Balloon, aircraft Satellite

Balloon, satellite, aircraft

Balloon, aircraft Balloon, aircraft Balloon

Rocket Rocket

Balloon, aircraft, ground

Balloon