ar 1 0.1h, where X is the free space wavelength. The thermal ...... Burke, W. 1., T. J. Schinugge and J. F. Paris, 1978, Comparison of 2.8 and 21 cm Microwave.
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^iI^
UASA Technical Memorandum 79606 N78 -332Q4
) -79r 1,;1INES (NASr. UiECT Of S I I> PA,:F 0 10 TF- MTCHC I; ;VF EMISSION FNrM SOTLS (NASA) 30 p itC A03 /"F A01 CSCL 20N
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34113 f
Effect of Surface Roughness on the Microwave Emission from Soils
B. J. Choudhury, T. J. Schmugge, R. W. Newton and A. Chang
.AUGUST 1978
Nationai Aeronautics and Space r7dministral,on
T^ i
Goddard Space Flight Center
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Greenbelt, Maryland 20-771
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11-1 : 1 ,1701 : S1 1 K1 ACC R0 11G11NUSS ON TI11-
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\11l'HOWAVI : I'MISSION FROM SOILS
I
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li 1.l'h,^u^lhtiry hn^u^'^tr I:. N'. Nr%%It'll
A. Ch.mg
r;
^^u„•. \`t, Cl IIlose rest IIIiilg from t I w agn it, illttit II prac-
tices of the two area.. The donunant method
of
irritation is flit• flooded furrow I he furrow
1i
separation waS about one nt etc r :IntI tIic furro\\ height \\ a. about 20 Cult. Stipctnnposed on these Corrugations \\ cre Clods, \\ 111L. 11
\\ ere
gcnC rally less than 5 Cll.
Plots of IF \cntis the soil moisture in various layers for the 1 0, : ,,nil I 07 ? flights .Ire presentcd in hi!tirc 4. We note Out the range of Fit is not as great as that e\peC fed for a "Illoolh surface.
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Calculations using the layered model (Wilhcit. 1978) were performed
using moisture i
and temperature profiles measured by the personnel at the U.S. Water Conservation Labortory at Phoenix (Jackson, 1973). The soil moisture and temperature profiles were observed at frequent intervals after it
irrigation on March2. 1971. These data from the same
area at flu sa •ie time of year were assumed to be reasonable estimates of the situations occuring during the 1972 aircraft overflights. It should be noted that the moisture and temperature profiles had been obtained from a smooth field, while the microwave radiometer results were obtained from rough-surfaced fields. The moisture profiles were rather uniform when wet, but dried rapidly at the surface after 5 or 6 clays producing sharp moisture and
y
i
dielectric constant gradients just helow Vie surface. The calculations were performed for I the early afternoon (1 :30 p.m.) profiles of each day. The corresponding temperature profiles
,I
are probably quite representative of the actual situation for the 1971 flights. For the 1973 flights, occurring early, in February, the teniIlerattires were somewhat cooler. The surface ;a
temperatures as observed by the aircraft IR S01150t were found to be about 15K lower than r
that ohscrved during lurch. The February temperature profiles were then obtained front the observed March temperature profiles by adjusting the gradient to fit the observed surface
i
temperature for February data and assuming two profiles to be equal at about 50 ent. The dielectric constants used in the calculation were those presented in I igt -c 1. These values are for soils having texture similar to the Avondale clay loam soil at t h e WaterC'onservation Laboratory.
i
'File solid curves in Fi g ure 4 are the calculated values assuming a sntm,th utrface (it 0). It is clear that the aircraft F B 's do not get as low as those calculated for the smooth surface. The form of the calculated curve however does agree with the observations i.e. little I
variation out to about 50% of Ft' and then the ra pid decrease in T,,. I
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^^ ^----••sr—^=. ^-.^.^La..^, _ -^;.-.,rte
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,
.l E
Pic dashed can-e-,
ill
4a. 1, and c are for h = 0.45 mill it is seen that the range
of
j
!
calculated I' ll 's is is good agrecn ► ent th0 observed rang .Ind that the roughncss factor has its
1
greAL'%I .'Ilea at the higher levels of mot%turc as predicted h. III. ( la). In observing the %ariation of T it %%ith soil moisture
ill
3 layers. we not. • the Imear
! ,
decrease 1' H with the `oil moisiur: in the 0-1 cnl laver. hilt for the 0-2.5 and 0-5 cnl layers
there is a region al
Io\%
soil moisture. for Miich Ihcrc is little variation of T it . Alime this
lc%cl there is a sharp dc.•rca>,c
ill
I tits hel ► al ior is similar to I l i-it 1)r0s0ntcd tit
and that the location of the hrcak I l k l int tile the :.5 .• m . • one, at approximately 50';• of FC.
is good ar..rccmcnt with
I11c location prom-mcd ill
igurc `. assuming a FC of 20- 25`^
I'm a
day l o ' lnl soil. liccause of this agreement, we ►VIII assunl0 that the radion ► 0tcr is responding to
the n ► oistul'r %anatlons Ili hil tlres J and
h
ill
1
top _' or 2.5 cm.
the restilts Irom the 1075 flights are pi cst, nted. figure 5 presents tllc
results from the pre-.I.mn Ilights and Figtlre h tronl ill y mid-da% Illhhls. hsentl.11k . Ilic S.Illll• depelldel ► cl•
Hit .
sured
ill
of 1
11 oil SMI moisture Is ollsmed IUr these
Illl'hts .1% for the
1 11 . t Illghts.
Dallies ► n I1 1 1.:au us0d the moisture mid temperature profiles that were mca-
field at the tin g e of the Ilights. Th0 rough surface curves area visual hest fit to
the calculated points. Note that the I' ll dil ' I 'erCllce 11OWTc11 Itit' ANI :Ind 1'M Ilights due to Soli tl• nlp0rit Ill k • changes is ex1+1ain0d h\ the calculations.
Tic hest agrccinctlt is obtained
ill
else for It 0.0 l ► hich is slighth larger than the
result fo g the 72 73 da1.1. I he reason for this dllfcrencr is unknown. and because of , the scaticr
ill
dat'i ma\ . indicale 1110 un6.0rtainl\ of our esomatcs for the \clue of Ii. Th0 scat-
ter in 1110 Lalcu1,11ed points ahout 1110 curves is due 10 two causes: first. the variations in the tillll Ilrioislllre
profiles having
the 5.1111: a%efagC U _' :I11 or t) 5 illl aVel':Igl•
lll0iStIIrC Icvels:
.11ld secondly . the Variations in soil temperature. 17
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SOIL MOISTURE, OF FIELD CAPACITY
Figuto
Aircraft observation of comp,ired with
1(^1 f^
111: soil
F I; at
= I.5; cm
Turin!, fli g ht o%cr I'llocilix
I oisluic In the surlac :m of the
'10
sell
, i
i i t
The values of h obtained for the aircrali data generally fall in between those obtained for the medium rough and rough cases for flit- field measurrni.-nt results (Figure i). This init
dicates that for the Phoeni y region none of the observed fields approached the smooth cutegory and an assumption that agricult ►lral fields are in the medium rough to rough (i.e. h 0.5) may be reasonable fur future calculations at this wavelength, I he data at 1.55 rill are presented in Figure 7. They are also described by an h of 0.6, the fact that h does not wale with wavelength is indicative of the shortcomings of the model In this cast-, it appear% that different portions of the roughness spectrum will contribute at the different 'Aavelengths.
II is also clear that ,erlam of our assumption concerning
the roughness are violated.
f
C'UNC'LUSONS A one parameter model for estimatin-, the effect of surface roughness on the microWave emission from soils his been developed and compared H ith radiometer measurements from
both tower and aircraft plall'Orms. B\ a suitable choice of the parameter. h, the model. %% hen conihincd %k,th a ra.ti.mve transfer model for the %oil. yields Rood agreenient with the observed brightness temperatures. An et •fective range ti► r the paranieter was found to be from 0 for a smooth surface to O.h for a rough glowed surfs... From the derivation of the
I i!
lie."_.
model the pmametcr It is expected to be proportional to the variance of the surface height. l however when compared with the measured variance for the tower measurements this dependence was not verified. A similar result was found in laboratory measurements of surface retlectivity (Hancock. 1 0 70. These latter measurennt-nts indicate that the horizontal scale Of surface roughness, i.e. surface slopes, is also important in determining, flit- magnitude of
1 the par,unrter h. Because of tlu, factor it does not appear possible to extrapolate the ralue
r +^
t
t
I
i
of It Itom the nkcjst;tc cnt% 1`li%ellle.t here at the 21 cm %%i%clolglll lt ► othel N.1\i1e11^11N
' I'
Jn.l iddiliolul meJ9urc • n110111% JI other \\ J\elenlah•
% 111 he tc.11111C I to
Jetellllm.` the .ICIVII
.1en ► e of It on -A j%dength, AI
the
21 on \\ .I%dotoIt ill. \.flue of 0 .5 for It .Il , he.lrs, t. ► t i c rciiicwIlt,lll\e r, ► f the con-
.11tloll ol-w1\.• .I Ill
I
111i .Itlir.11t J.It.I
owl the .11'll^lllluti l .Ili.l .110i111.1 I'lloelll\.
hereloti \\ IIIt this Illodd lot rotll;hiw%% I.IJ1.111\i tian-iler Illodel ". ak- llJtiol1% --hould \ Idd
liillrJte e^11 ►il.lte^ .`t 111 ` \Jlties .it i It
Ior
.1 \\ I.le IJlhe . ► f Il omure Jnd (.`nlh iatuli
"on.1 ► t lolls.
l urtha Noll. Atli hr re.lulrm to .le lrrnrine the \ ► .1\.•L•n^th .IcpcnJ.'nie 01 , 11 .InJ to J: telmille 11 till• illodel i.11l .liiu1.11e1) 1 1 hAllil 111e 1 1 ol.111IJtloll Jillerellii% i \1 l iiled h► 1 ott-
11 i.\UNi.i Ik^^tt ^I I lie 1 0-5 data Hire .ioluired h\ the Illi 1111`os. ► I Joint ^% oll M.`mm' I \pC11111i111 \\ 1101
A &M ( mwlstl) .Ill.l
111w1wd 111\ CSItg.Itols tion)
It , \ASA.
111e1r i.`. I ` i i,ltl\ 1 11 Ill
Ii A1111; 111CM'
.`1 \Ikon--as III ,IJJ1lloll MS 1% .IhhliilJli ►I.
1Z I I l I: I V(' Anion t. fit!
\
I` l ` :
I . o \\ ,Iid% A I
hio1\ of I2ellcoton B\ A
Rough Silll.lie,
o
IRI-, \.+1. 41 , v. I4_'-14c•.
lt.11rick. 11 1 . 1 .1- 0. ul -R.1J.n Ccos: Section H.111.ihook - . \t ► I. _, I'ditor
G I Wt1A.
11 '. 11L.111 Pic%%, N .Y. It"111, N. and I'. \ ,At. 1 0 '^ "Pti i11► lea
Chapt:l \III V lg.lmon. \. ) .
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L
Burke, W. 1., T. J. Schinugge and J. F. Paris, 1978, Comparison of 2.8 and 21 cm Microwave Radiometer Observations ever Soils with Emission Model Calculation, Journal of Geophysics: Research, (to be published). Chandrasekhar, S., 1960. "Radiative Transfer", Dover, N.Y. England, A. W., 1976, Relative Influence upon Microwave Emissivity of Fine-Scale Stratigraphy, Internal Scattering and Dielectric Properties, Pure and Applied Geophysics,
vol. 114, p. 287-289. Ilancock,G. D., 1976, Broad Spectrum Microwave Measurements of Vugh Discontinuous Surfaces for the Determination of Moisture Content, Department of Electrical Engi-
neering, University of Arkansas, Arkansas 72701. Jackson, R. D.. 1973. Diurnal soil-water content charges during drying, Field Solar Water Regime, SSSA Special Publication 5, pp. 37-56, Soil Sciences Society of America,
Madison, Wisconsin. Lundien, J. R., 1971, Terrain Analysis by Electromagnetic Means, U.S. Army Waterways Experiment Station, Technical Report No. 3-693, Report 5. Newton, R. W., 1977, Microwave Remote Sensing and its Application to Soil Moisture Detection, Technical R!port RCS-8l of the Renu,te Sensing Center of Teas A&M University, College Station, Texas, Available from University Microfilms order No. 7720-398.
Njoku, E. G. and I. A. Kong, 1977, Theory for Passive Microwave kemote Sensing of NearSurface Soil M oiStUre, Journal of Geophysical Research, vol. 82, p. 3108-31 17. t
Schmugge, T. J., T. T. Wilheit, W. Webster, and P. Glorsen, 1976a, Remote Sensing of Soil
i
Moisture with Microwave Radiometers 11, NASA Technical Note, TN D-8321. ;f
23
i t 5
f A"
7
(
T
•'.^^
.:s;._t ^-^
^
I
SchniugKe,T. 1., 19761)• Preliminary Results from the March 1975 Soil Moisture Flight,
Goddard Space Flight Center, NASA X-913-76-216. Schntugge, T., 1978, Effect of Soil Texture on the Microwave Emission of Soils. To be published.
Sung, C. C and W. D. Eberhardt, 1978, Explanation of the Experimental Results of Light Backscat(cred from a Very Rough Surface, Journal of Optical Society of America vol. 68, p. 323 -328. Tolstoy, 1. and C. S. Clay, 1966, "Ocean Acoustics McGraw-lull, N.Y.
Tsang, L., E. Njoku and J. A. Kong.. 1975, Microwa%c Thermal Emission from a Stratified Medium with Non-uniform Tempera ► .tre Distribution, Journal of Applied Physics, Vol. 46, pp. 5127-5133.
Waite, W. P., K. R. Cook and 13. B. Bryan, 1973, Broad Spectrum Microwave System for Remotely Measuring Soil Moisture Content, Publication No. 18, Water R,sources Research Center, University of Arkansas, Arkansas 72701. Wang, J., T. Schniugge. and 1). Williams. 1978, Dielectric Constants of Soil Microwave Frequencies - 11, NASA Technical Paper TP-1 238. Wilheit, T., 1978, Radiative Transfer in a Plane Stratified Dielectric. IEEE Transactions of Geoscience Electronics, vol, GE:-16, p. 138-143. Wu, S. T. and A. K. Fung, 1972, A Non-Coherent Model for Microwave Emissions and
Backscattering from Sea Surface, JoUr:al of Geophysical Research, vol. 77, p. 5917-
5929.
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