Subvisible cirrus clouds (SCi) were easily distinguished in mid-infrared (MIR) TIROS-N daytime data from south Texas and northeast Mexico. The MIR (3.55-3.93 micrometer) pixel digital count means of the SCi affected areas were more than 3.5 standard deviations on the cold side of the scene means. (These standard deviations were made free of the effects of unusual instrument error by factoring out the Ch 3 MIR noise on the basis of detailed examination of noisy and noise-free pixels). SCi affected areas in the IR Ch 4 (10.5-11.5 micrometer) appeared cooler than the general scene, but were not as prominent as in Ch 3, being less than 2 standard deviations from the scene mean. Ch 3 and 4 standard deviations and coefficients of variation are not reliable indicators, by themselves, of the presence of SCi because land features can have similar statistical properties

Johnson, M. P.

Nixon, P. R.

Richardson, A. J.

Wiegand, C. L.

English

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E82-1029 5
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METHODS OF EDITING CLOUD AND ATMOSPHERIC LAYER
AFFECTED PIXELS FROM SATELLITE DATA
Principal Investigator:
Co-Investigators:
Paul R. Nixon
Craig L. Wiegand
Arthur J. Richardson
Michael P. Johnson
Agricultural Research Service
U.S.. Department of Agriculture
P. 0. Box 267
Weslaco, TX 78596
(E82-10295) 8E1dODS OF ELZIING CLOUD AbD	 N82-21571
ATMOSPHERIC LAYER AEFFCTEL PlYELS FfiCh
SATELLITE DATA ,duarterly Pzogress Eeport, 5
Dec. 1981 - 5 Aar. 19E2 (Agricultural	 Unclas
Research Service) 7 1 HC A02 /HF Av1	 G3/4J 00295
March 1982
Type Ii Quarterly Progress Report, Number 5
for Period December 5, 1981 to March 5, 1982
Prepared for
GODDARD SPACE FLIGHT CENTER
Greenbelt, MO 20771
RECEIVED
MAR 2 4, / 'y $ 2
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	 2. Gaeeeemewt Accossien lie. 	 _. Recipient's Cosdp W.
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MENODS OF EDITING CLOUD AND ATMOSPHERIC LAYER 	 ` March 1
AFFECTED PIXELS FROM SATELLITE DATA	 i. Ped:..i.g oyeei:e"" core
7. Aushoe(s)
Pau1_R_ Nixon. at al-
s_ pedeeadag orrsi:er"s Repoli Ne.
9 P"femd" orrA 1io - "oat ea Address	 Meek wit me.i19.
t Agricultural Research Service
U.S. Department of Agriculture 11. a••.•te... P"t N..S-75406-BP. 0. Box 267
	 13. Type of Repoo a" P*rW Covw4
112. Uomori.+ Arwcy go" end A46"s	 TYPE 11 REPORT
GDODARD SPACE FLIGHT CENTER	
12/5/81-to 3/5/82
Greenbel t,. MD
	
20771	 14. Spensering A,geocy code
U. SomAonowevey tyres
16. Absrete!
Subvisible cirrus clouds (SCi) were easily distinguished in mid-infrared
MIR) TIROS-N daytime data from south Texas and northeast Mexico. 	 The MIR
3.55-3.93 )Am) pixel digital count means of the SCi affected areas were
more than 3.5 standard deviations on the cold side of the scene means.
(These standard-deviations were made.free of the effects of unusual
instrument error by factoring out the Ch 3 MIR noise on the basis of
detailed examination of nois	 and noise-free pixels). 	 SCi affected areas
in this IR Ch 4 (10.5-11.5 ;1 appeared cooler than the general scene, but
were not as prominent as in Ch 3, being less than 2 s tagdard deviations
from the scene mean.	 Ch 3 and 4 standard deviations and coefficients of
variation are not reliable indicators, by themselves, of the presence of
SCi because land features can have similar statistical p.-operties.. .
7. Key Worts (S, itcteJ by Awther(s)) 18.Oistribution Stott-smat
Heat Capacity Mapping .Mission, HCMM,
Clouds, Cloud Screening, Terrestrial
Reflectance, Terrestrial Radiation,
Atmospheric Sounding
9. Secwity Clessif. (of this report) 20. Secwity Clossif. (of this page) 21. me. of Pages 22. Pekoe
UNCLASSIFIED UXCLASSI FI ED
. n!
`i
3. TYPE II QUARTERLY PROGRESS REPORT
Report Number 5
December 5, 1981 to March 5, 1982
A. Problems:
Slow progress in locating suitable data for analysis.
B. Accomplishments:
1. Satellite Mid IR * Channel Clearly Detects Subvisible Cirrus Clouds
Absorbing-emitting atmospheric layers that are essentially trans-
parent in the visible wavebands commonly occur in our south Texas
and northeastern Mexico test area, especially in the summer months.
We refer to these layers as subvisible cirrus (SCi) .
Examination of the TIROS-N 06 May 79 daytime test area scene on a
I2S Image Processing System showed the presence of SCi as areas of
colder than expected temperatures in Channel (Ch) 3 (3.55-3.93 PM)
and Ch 4 (10.5-11.5 um) data. These SCi areas were centered at
98.7°W longitude, 25.4°N latitude in Mexico, and 98.6°W, 27.3°N in
Texas. Except for SCi, the test area had no clouds.
A problem with TIROS-N has been noise in Ch 3 data. Display of
Ch 3 on the image processing system showed the expected features
of a mid-infrared (MIR) scene. However, close inspection revealed
noise characterized by one or more "noise-free" scan lines followed
by noisy 1 i nes , followed by noise-free 1 i nes , etc. By noise-free,
we mean free of unusual instrumentation errors. The noise-free and
noisy lines did not generally prevail across the entire scene, but
frequently changed from one class to the other, one or more times
along the scan. To test if Ch 3 could be used in our study of SCi,
we identified a noise-free 140 pixel area in the Gulf of Mexico for
comparison with a nearby 450 pixel noisy area. The mean Channel 3
counts were 625.? and 620.0, respectively; not greatly different,
considering the possible effect of Gulf currents. A similar com-
parison of adjacent noise-free and noisy Ch 3 data in Texas (each
less than 76 pixels) gave means of 456.8 and 459.0. These suggest
that mean values for a given landscape feature are representative
of the feature whether they come from noise-free, mixed or noisy
data, provided the sample is large enough. However, the standard
deviations did vary markedly between noise-free and noisy data.
They were 10.6 and 62.6 counts, respectively, for the Gulf of
Mexico, and 18.8 and 78.0 for the land area.
4The relation of TIROS-N data from selected areas of south Texas and
northeastern Mexico to the scene as a whole is shown in Fig. 1. The
four axes represent the channels of satellite data, and are identi-
fied by channel nucber. Digital counts for the various channels
Increased froai the center of figure outward (64 counts/in for Ch 1
and Ch 2 9 160 counts/in for Ch 3 and Ch 4). The lines and shading
beb,aen axes have no meaning except to guide the eye from comparable
data in one channel to that in another.
The shaded area represents all data of the stuo+y area (over 170,000
Pixels) that fall within 3 2 standard deviations of the mean. The
standard deviations of "noise-free" Ch 3 for the scene and areas
of interest were estimated by prorating on the basis of 65% of the
available data being noisy, according to the characteristics dis-
cussed above for the land area.
Shown in the figure are mean digital counts from SO affected areas
in Mexico and Texas, and their corresponding nearby nonaffected
areas. Each of these four areas exceeded 700 pixels. In Ch 1
(0.55-0.90 um) and Ch 2 (0.725-1.10 um) the SO and clear areas all
fell well within the 3 2 standard deviations of the entire area.
In Ch 3, the non-SCi-affected areas fell in the center of the shaded
area indicating that they were close to the mean o that channel for
the entire test area. However, in Ch 3, the SO areas in Mexico and
Texas were very different from the other features, being more than
+3.5 standard deviations from the scene mean. Clearly, the MIR
(Ch 3) distinguished the SO condition from the non-SCi-affected land
features.
In Ch 4, the non-SCi-affected area was close to the mean of the
Texas-Mexico test area. However, it can be seen in Fig. 1 that the
SO areas were indicated as colder than the test area mean, but
deviated from it by less than 2 standard deviations.
2. Coefficient of Variation is Un
Examination of thermal pixel values of a HCMM south Texas scene for
the freeze night of 03 Jan 79 showed that in subvisible cirrus cloud
(SCi) affected areas, the standard deviations and the ratios of
standard deviations to the means were small in comparison with those
in clear non-SCi areas (Wiegand, C. L., et al.)'.
1 Wiegand, C. L., et al. Plant Cover, Soil Temperature, Freeze, Water
Stress, and Evapotranspiration Conditions. Type III Final Report prepared
for Goddard Space Flight Center. February 1981.
t
5These differences were not as prominent in an investigation of
TIROS-N daytime data of SO and clear areas in Texas and Mexico
(first four data columns of Table 1, same areas discussed in pre-
vious section). While the MIR (Ch 3) and IR (Ch 4) showed less
variability in the SO areas than their adjacent clear areas, the
difference was slight in the Ch 4 Texas data. Furthermore, in Ch
4, the standard deviation and coefficient of variation were greater
in the SO area of Mexico than the clear area of Texas (both part
of the same satellite scene). The Ch 3 standard deviations of
Texas clear and Mexico SO are quite similar. Thus, use of standard
deviations or coefficients of variation must be discarded as a
method, in itself.-of screening for SCi .
C. Significant Results:
Subvisible cirrus (SO) cloud conditions can be distinguished from non-
SO conditions in meteorological satellite mid-IR (3.55-3.93 um) data.
D. Publications:
None
E. Recommendations:
None
F. Funds Expended: (through 28 Feb 1982)
Allotment for FY 82 ------- ----------------------
Location and indirect program costs----
Salaries ------------------------------
Travel and transportation -------------
Transportation of things -•------------
Services, supplies and equipment ----
Totalexpenditures -------------------------
Bal ance
G. Data Utilfty:
We are using the same HCMM data sets for this study as were used for
the initial HCMM contract. The data are of good quality. Examples
of subvisible cirrus clouds (SCi) have been found in TIROS-N data.
Noise in Ch 3 (3.55-3.93 pm) caused problems in the investigation of
SO screening methods. The mean pixel values of TIROS-N Ch 3 data
appear to be approximately correct, as the errors seem to be
distributed about the true mean.
. '	 6
Table 1.	 Spectral charrcteristics of selected features of a 06 May 79 TIROS-N
scene.
Gulf
Texas Mexico of Southeast Colorado
3ci	 ear ` sci	 ear Mexico Cloud a ow	 ear
Channel 1 (0.55-0.90 um)
Mean 125.3 127.7 111.1 119.8 56.8 281.8 76.6 148.3
Mode 124.0 128.0 108.0 112.0 56.0 276.0 68.0 148.0
Median 124.7 127.6 109.6 116.9 56.5 286.0 73.2 147.9
Std. dev. 5.24 4.40 11.56 11.88 1.60 51.04 9.08 3.83
Coef. of var. 1 .042 .034 .104 .099 .028 .181 .119 .026
No. of pixels 1157 1168 702 956 816 46 41 65
Channel 2 (0.725-1.10 um)
Mean 158.2 155.1 141.3 141.0 48.0 279.4 74.0 159.6
Mode 156.0 156.0 136.0 136.0 48.0 304.0 64.0 156.0
Median 157.4 155.2 140.3 139.5 48.0 282.0 70.0 158.5
Std. dev. 7.16 5.92 13.20 12.00 .56 45.12 10.52 4.76
Coef. of var. .045 .038 .093 .085 .012 .162 .142 .030
No. of pixels 115? 1168 702 956 816 46 41 65
Channel 3 (3.55-3.93 um)
Mean 439.7 287.3 506.2 295.0 625.2 559.3 522.2 200.7
Mode 43?.0 320.0 532.0 324.0 632.0 380.0 532.0 188.0
Median 442.8 289.1 512.4 304.8 625.6 565.6 530.8 197.0
Std. dev. 2 17.36 22.48 21.64 33.88 9.36 22.36 12.36 12.52
Coef. of var. .040 .078 .043 .115 X15 .040 .024 .062
No. of pixels 1157 1168 702 956 316 46 41 65
Channel 4 (10.5-11.5 um)
Mean 383.5 339.2 408.7 344.4 443.4 730.7 400.1 335.3
Mode 384.0 340.0 416.0 352.0 444.0 796.0 396.0 328.0
Median 382.6 337.1 406.4 342.1 443.6 158.0 397.4 332.0
Std. dev. 7.88 8.52 17.00 20.32 1.72 75.84 22.12 10.20
Coef. of var. .021 .025 .042 .059 .004 .104 .055 .030
No. of pixels 1157 1168 702 956 816 46 41 65
1 All coefficients of variation in this table are expressed as decimal fractions.
2 Standard deviation adjusted by removal of estimated instrumentation noise.
ORIGINAL PAGE IS
OF POOR QUALff Y
CH3
•
rr:: .	 ...
..•
i::S.	 l N
F?ti, ,
	
V	 a ' ^•.•• rr' ::
CH2'.'.--^.•.'•	 ^'`'	 4-BRIGHT	 COLD -^
	
CH4
•••f••	 x0X
	
w,•,,
r	
--- - — MEXICO SCi
..	 --- - - — MEXICO Clear
CH 1
	
	
TEXAS SCi
--- — TEXAS Clear
Fig. 1. Mean digital values in four spectral channels (- Ch) of .
clear and subvisible cirrus (SCi) affected areas, - ntd
the ran of values between t 2 standard deviations
(shaded in the 110,000 pixel test area of south Texas
and northeast Mexico. TIROS-N daytime 06 May 79.


Methods of editing cloud and atmospheric layer affected pixels from satellite data

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