An airborne multispectral scanner was used to obtain data over two adjacent cotton fields having rows perpendicular to one another, at three times of day (different solar elevations), and on two dates (different plant size). The near IR/red ratios were displayed in image form, so that within-field variations and differences between fields could be easily assessed. The ratio varied with changing Sun elevation for north-south oriented rows, but no variation was detected for east-west oriented rows

Goettelman, R. C.

Jackson, R. D.

Leroy, M. J.

Millard, J. P.

English

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Early Warning and Crop
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A Joint Program for
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Remote Sensing
August 1981
AIRBORNE OBSERVED SOLAR ELEVATION AND ROW
DIRECTION EFFECTS ON THE NEAR-IR/RED RATIO OF COTTON
J. P. Millard, NASA/Ames Research Center
R. D. Jackson, USDA-ARS
R. C. Goettelman, EAL Corporation
M. J., LeRoy, DCA Corporation
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1, Report No, 2. Government Accession No 3. Reci pient's Catalog No
JSC-174211;	 EW-111-041 h4
4. Title and Subtitle 6. Report Data
Airborne Observed Solar Elevation and Row N rection August 1981
Effects on the Near-IR/Red Ratio of Cotton 6. Performing Organiratton Code
7. Author(s)
Millard, J.	 P., Jackson,	 R.	 D., Goettdntan, R.	 C.,	 and
8, Performing Orgamtanon Report No.
LeRoy, M. J.
10. Work Unit No.
0. Performing Organization Name and Address
NASA/Alves Research Center, Moffett Field, California
USDA/ARS, U.S. W Ler Conse 	 nt:ion Laboratory, Phoenix, AZ 11. Contract or Grant No
13. Type of Report and Period Covered
Research Results
12. Sponsoring Agency Name and Address
NASA and USDA
AgRISTARS/Earl y Warninq/Crop Condition Assessment
14, Sponsoring Agency Code
1050 Bay Area BI vd, , Houston . Texas	 r
15. Supplementary Notes
16, Abstrw
An airborne multis pectral	 scanner was used to evaluate sun elevation and vow direction
effects on the near-lR/red ratio of cotton.
	
Data were obtained with a Daedalus DEI 1260
multisaectral
	
scanner over two adjacent cotton fields, one with east-west oriented rows
and the second with north-south oriented rows.
	
The ;ear-IR/red ratios were displayed
in inlage farm, so	 that within-field variations and differences between fields could be
easily assessed.	 The near-lR/red ratio varied with changing sun elevation (time of day)
for north-south oriented rows, but no variation was detected for east-west oriented rows.
17. Key Words (Suggested by Author(s)) 18. Distribution Statement
Airborne Multispectral	 Scanner
Sun Elevation
Row Direction
Cotton
Near-IR/red Ratio
i9. Security Classif. (of this report) 20, Security Classif. (of this page) 21.	 No. of Pages 22. Price
Unclassified Uncl assified
'For sale by the National Technical Information Service, Springfield, Virginia 22161
JSC Form 1424 IRev Nov 751
	
NASA — JSC
AIRBORNE OBSERVED SOLAR ELEVATION
AND ROW DIRECTION EFFECTS
ON THE NEAR-IR/RED RATIO OF COTTON
..
I
PRINCIPAL INVESTIGATORS
J. P. Millard
R. D. Jackson
R. C. Goettelman
M. J. LeRoy
APPROVED BY:
a
Glennis 0. BoatviriPt
Early Warning/Crop Condition Assessment Project
AgRISTARS Program
Earth Observation Division
Space and Life Science Directorate
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
L,YNDON B. JOHNSON SPACE CENTER
HOUSTON, TEXAS
August 1981
AIRBORNE OBSERVED SOLAR ELEVATION AND ROW DIRECTION EFFECTS
ON THE NEAR-IR/RED RATIO OF COTTON
J. P. Millard,Y R. D. Jackson,?/
 R. C. Goettelman,3/ and M. J. 'LeRoy4/
ABSTRACT
An airborne multispectral scanner was used to evaluate sun elevation
and row direction effects on the near-IR/red ratio of cotton. Data were
obtained with a Daedalus DEI 1260 mul.tispectral scanner over two adjacent
cotton fields, one with east-west oriented rows and the second with north-
south oriented rows. The near-IR/red ratios were dispiayed in ?,mage form,
so that within-field variations and differences between fields c)uld be
easily assessed: The near-IR./red ratio varied with changing sun elevation
(time of day) for north-south oriented rows, but no variation was detected
for east-west oriented rows.
I/ NASA/Ames Research Center, Moffett Field, California.
2/ USDA/SEA/AR, U. S. Water Conservation Laboratory, Phoenix, Arizona.
3/ EAL Corporation, Richmond, California.
4/ DCA Corporation, Palo Alto, California.
s
1
u,;
PRECEDING PAGE BLANK NOT FILMED
2
INTRODUCTION
Multispectral data acquired in the red and near^-IR portions of the
electromagnetic spectrum have potential for use in agricultural crop
assessment. Combinations of these two bands have been related to leaf area
index and green biomass (Wiegand et al., 1979; Tucker, 1979; Colwell et
al., 1977; Pearson et al., 1976; and Haas et al., 1975). They have also
I	 been used for yield estimation (Rase and Siddoway, 1981; and Idso et al.,
1980).
The amount of reflected solar radiation received by a sensor above a
row crop is affected by sun elevation and row direction (Jackson et al.,
1979b). This effect occurs as a result of changing amounts of solar
irradiance, changing fractions of sunlit and shaded soil, and changing
fractions of sunlit and shaded vegetation. Duggin (1977) and Jackson
et al. (1979a) demonstrated the effect of sun elevation on spectral data
utilizing nadir oriented, ground-based radiometers over wheat. Jackson
et al. (1979a) demonstrated that the near-IR/red ratio changed considerably
with sun elevation for north-south oriented rows. To the author's
knowledge these effects have not been documented for aircraft data.
This report presents results of an experiment in which an airborne
scanner was used to obtain multispectral data over two fields having rows
perpendicular to one another, at three times of day (different solar
elevations), and on two dates (different plant sizes). The data were pro-
cessed into images of the near-IR/red ratio.
3E'
3EXPERIMENTAL
Flights were made over two adjacent cotton fields located about 40
kilometers south, of Phoenix, Arizona on 12 June and 12 July 1979. The east
field had one--meter spaced rows of cotton running north and south, and the
Crest field had similarly spaced rows running east and west. At the time of
the 12 June flights the cotton was about 27 cm high and 25 cm wide. Ground
cover was estimated at 25%. By 12 July the plants were about 73 cm high
and 64 can wide, covering about 62% of the soil.
Measurements were made with a Daedalus DEI 1260 multispectral scanner 	 j
from a nominal altitude of 914 meters. The scanner had 11 channels, ten in
the visible/near -lR region and one in the thermal-IR. The wavelengths used
in this paper are: (a) 0.600 - 0.650 pm (red); and (b) 0.800 - 0.850 um
(near-IR). Two scan configurations were available. On 12 June, the
scanner had an instantaneous field-of-view of 2.50 mrad and a total scan
angle of 84% On 12 July, the scanner had an instantaneous ,field-of-view
of 1.25 mrad and a total scan angle of 42% Images were produced as
described by Millard et al (1978).
RESULTS AND.CONCLUSIONS
Field averages of the near-IR/red ratios for the two dates are plotted
in Figure 1 versus solar elevation. Also included is a scale to relate
time of day to solar elevation. Field averages were computed from data
acquired on the east-west flight track. On 12 June, when the plants were
small the near--IR/red ratio was independent of solar elevation and row
direction. On 12 July, when the plants were more mature, solar elevation
4
e^,
Phad a marked effect on north-south planted rows but little effect on east-
west rows. Figure 2 shows near-lR/red images of the two fields for two
times of day on 12 July 1979. The effect of time of day is quite dramatis,
for the north-south planted rows (east field). For the 8:57 a.m. flight
the east field near -IR/red average is about 4.5 whereas the 12:33 p.m.
image yields a value of about 2.8. Tile near-Ip/red image of the east-west
planted rows (west field) is nearly independent of time of day.
An explanation of why the near-IR/red ratio changed with time of day,
or solar elevation, over the north-south planted rows (east field), can be
obtained with the aid of figure 3. This is a plot of radiance in the red
and near-IR channels for the 8:57 a.m. and 10:47 a.m. flights on 12 July.
The red radiance increased about 60% from 8:57 a.m. to 10:47 a.m., whereas
the near-IR radiance increased only about 30%. An increase of about 30%
could be expected in both channels due to increasing solar irradiance. The
red channel, however, increased significantly more because early--morning-
F
shadowed soil became sunlit. The near-IR radiance did not exhibit the same
4i
"shadow" efferts because green plants are partially transparent in the
near-IR (Tucker, 1977; and Gausman et al., 1973). The combined effect was
to lower the near-IR/red ratio with increasing sun elevation. For the
east-west planted rows the soil was mostly sunlit throughout the entire day
at the location and time of year of this experiment. Thus there was Less
of a "shadow" effect and both the red and near-IR radiances increased in
'	 about the same proportion as solar irradiance.
5
5The results presented here demonstrate the degree to which row orien-
tation and solar elevation can influence aircraft measurements of
near--IR/red ratios. They also suggest that multiapectral data acquired at
several times of day may be useful for evaluating crop parameters such as
plant cover and row orientation (Jackson et al., 1979b).
ACKNOWLEIDGMF,NTS
We thank Drs. R. J. Reginato and P. J. Pinter, Jr., of the U. S. Water
Conservation Laboratory, Phoenix, Ar4",wona, for providing the ground data.
6
6REFERENCES
Aase, J. K. and F. H. ''iddoway. "Spring wheat yield estimates from spectral
reflectance measurementsy" ?1;EE Trans. Geo. Sci. & Remote Sensing,
GE-19:78-84 0 1981.
Colwell, J. E., D. P. Rice and R. F. Nalepta. "Proceedings of the Eleventh
International Symposium on Remote Sensing of Environment"
(Environmental Research Institute of Michigan, Ann Arbor, 1977),
Vol. 2, p. 1245.
Duggin, M. J. "Likely effects of solar elevation on the quantification
of changes in vegetation with maturity using sequential Landsat
imagery," Applied Optics 16:521-525, 1977.
Gausman, H. W. and W. A. Allen. "Optical parameters of leaves of thirty
plant species." Plant Physiol. 52:57-62, 1973.
Haas, R. H., D. W. Leering, J. W. Rouse, Jr., and J. S. Schell.
"Proceedings of NASA Earjh Resources Survey Symposium." (NASA,
Washington, D. C., 1975), Vol. 1, p. 42.
Idso, S. B., P. J. Pinter, Jr., R. D. Jackson, and R. J. Reginato.
"Estimation of grain yields by remote sensing of crop senescence
rates," Remote Sensing of Environment 9:80-91, 1980.
Jackson, R. D. , P. J. Pinter, Jr., S. B. Idso and R. J. Reginato.
"]heat specular reflectance: interactions between crop configuration,
sun elevation, and azimuth angle," Applied Optics 18:3730-3732, 1979a.
Jackson, R. D., R. J. Reginato, P. J. Pinter, Jr., and S. B. Idso.
"Plant canopy information extraction from composite scene reflectance
of row crops," Applied Optics 18:3775-3782. 1979b.
7
7Millard, J. P., R. D. Jackson, R. C. Goettelman, A. J. Reginato and
S. B. xdso. "Crop water-stress assessment, using an airborne thermal
scanner," Photogramtetric Engineering and Remote Sensing 4-4:77-85,
1978.
Pe4rson, R. L., L. D. Miller, and C. J. Tucker, "Hand-held spectral
radiometer to estimate gramineous biomass," Appl. Opt. 15:416-418,
1976.
Tucker, C. J., "Asymptotic nature of grass canopy spectral reflectance,"
App1. Opt. 16:1151-1156, 1977.
Tucker, C. J., "Red and photographic infrared linear combinations for
monitoring vegetation," Remote Sensing Environ. 8:127--150 0 1979.
W egand, C. L., A, J. Richardson, and E. T. Kanemasu, "Leaf are index
estimates for wheat from Landsat and their implications for
evapotranspiration and crop modeling," Agron. .T. 71:336-342, 1979.
f 1#	 a
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LIST OF FIGU S
Fig. 1. Field averaged near-IR/red ratio versus jolar elevation and time
4
of day: N-S and E-W row orientations on two dates corresponding
4
to different percent canopyP	 PY oovers.
Fig. 2. Near--IR/red images acquired 12 July 1979; fli6 t direction is
from east to west (north is the top of page).
a. 8:57 a.m.
b. 12:33 p.m.
Fig. 3: Radianoe in the red and near-IR channels versus angle of view for
two times of day.
P
51i
4
N'SRo
^L'GR'^NT
0gT^N
12 JULY DATA (62% COVER)
G	 E-W ROW ORIE -ITATION ..
a3
	
.
0W
Q
Q2W
N-S AND EW ROW ORIENTATION
1	 12 JUNE DA'TA , (25%o COVER)
30	 40	 50	 60	 70	 80	 90
SOLAR ELEVATION
1	 (	 '	 (	 1	 1
8 a.m./4 p.m,
	 9 a.m./3 p.m.	 10 a.m./2 p.m. 11 a.m./1 p.m. 12 noon
LOCAL STANDARD TIME
4
OnIGINAI_ PA07
Lit ACK AND WHITE PHOTOGRAPH
S	 S
Figure 2
W-,
NASA=JSC
50
10:47 a.m.
40
d NEAR- IR
H
E 30	 .^
N
E	 8:57 a.m.
4
20
u
'E	 10:47 a.m.
10	 RED	 r
8:57 a.m.
0	 =
-25	 -20	 -15	 -10	 ,5	 0	 5	 10	 15	 20	 25
DEGREES FROM NADIR
Figure 3


Airborne observed solar elevation and row direction effects on the near-IR/red ratio of cotton

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