Transcript Sensitivity of Off-Nadir Zenith Angles to Title the Surface Reflectance Ratio Technique

Sensitivity of Off-Nadir Zenith Angles to
Title
the Surface Reflectance Ratio Technique
EOS
Michael D. King,1 Charles Gatebe,1,2 Si-Chee Tsay,1
Qiang Ji,3 Tom Arnold,4 and Jason Li4
1NASA
Goddard Space Flight Center
2University of Maryland Baltimore County
3Science Systems and Applications, Inc.
4SM&A Corporation
Outline
 Spectral variation of surface reflectance over land
– Important for the retrieval of aerosol optical thickness over land
Michael D. King, EOS Senior Project Scientist
1
July 3, 2000
Goals &Title
Objectives
EOS
Data Set Used
 Cloud Absorption Radiometer (CAR) data
– Smoke, Clouds, and Radiation-Brazil (SCAR-B), August-September 1995
Strategy Used
 Select a pristine case
– Plot reflectance R0.47(0.67) as a function of R2.20 for view angles from
nadir to 65° and then compute the slope, correlation coefficient r,
and intercept from the best line of fit
– Plot the slope of reflectance as a function of zenith view angle
from 0–65°
– Repeat for different solar zenith angles—forward scattering
direction
 Select high turbidity case and repeat
 Do atmospheric correction using 6S for different aerosol optical
thickness
 Explore R0.47(0.67)/R2.20 for all azimuthal angles from BRF
measurements
Michael D. King, EOS Senior Project Scientist
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July 3, 2000
University of Washington
Title
CV-580
EOS
Michael D. King, EOS Senior Project Scientist
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July 3, 2000
Cloud Absorption
Title Radiometer
EOS
 Goddard Space Flight Center
– developed in 1982-1983
 University of Washington
– integrated & flown in 1984 (B-23)
– principal data from 1987-97 (C131A)
– flights after 1998 (CV-580)
 Sensor Characteristics
– 14 spectral bands ranging from
0.34 to 2.29 µm
– scan ±95° from horizon on righthand side of aircraft
– field of view 17.5 mrad (1°)
– scan rate 1.67 Hz (100 rpm)
– data system 9 channels @ 16 bit
– 395 pixels in scan line
– 4% reflectance calibration
accuracy
Michael D. King, EOS Senior Project Scientist
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July 3, 2000
Cloud Absorption
Title Radiometer
EOS
Horizontal mode
Michael D. King, EOS Senior Project Scientist
Vertical mode
5
July 3, 2000
Scatter Plots of Reflectance at 0.47 and
0.67 µm as a Function
Title
of Reflectance at 2.2
µm
EOS
Brasilia
q = 30°
f = 132.1°
Reflectance (0.47 µm & 0.67 µm)
q = 0°
Reflectance (2.20 µm)
Michael D. King, EOS Senior Project Scientist
Reflectance (2.20 µm)
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July 3, 2000
Reflectance Ratios R0.47/R2.20 and R0.67/R2.20
Title
as a Function of View Zenith Angle
EOS
R0.47(0.67)/R2.20
Brasilia
Aircraft height above ground = 2.4
km
q0 = 45.4°
f = 132.1°
R0.67/R2.20
R0.47/R2.20
Zenith Angle
Michael D. King, EOS Senior Project Scientist
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July 3, 2000
Reflectance Ratios R0.47/R2.20 and R0.67/R2.20
Title
as a Function of View Zenith Angle
EOS
R0.47(0.67)/R2.20
Cuiabá
Aircraft height above ground = 2.0
km
q0 = 54.1°
f = 109.3°
R0.67/R2.20
R0.47/R2.20
Zenith Angle
Michael D. King, EOS Senior Project Scientist
8
July 3, 2000
Reflectance Ratios R0.47/R2.20 as a Function
of Zenith AngleTitle
with Atmospheric
Correction
EOS
R0.47/R2.20
Brasilia
Aircraft height above ground = 2.4
km
q0 = 45.4°
f = 132.1°
Zenith Angle
Michael D. King, EOS Senior Project Scientist
9
July 3, 2000
Reflectance Ratios R0.67/R2.20 as a Function
of Zenith AngleTitle
with Atmospheric
Correction
EOS
R0.67/R2.20
Brasilia
Aircraft height above ground = 2.4
km
q0 = 45.4°
f = 132.1°
Zenith Angle
Michael D. King, EOS Senior Project Scientist
10
July 3, 2000
Reflectance Ratios R0.47/R2.20 as a Function
of Zenith AngleTitle
with Atmospheric
Correction
EOS
R0.47/R2.20
Cuiabá
Aircraft height above ground = 2.0
km
q0 = 54.1°
f = 109.3°
Zenith Angle
Michael D. King, EOS Senior Project Scientist
11
July 3, 2000
Reflectance Ratios R0.67/R2.20 as a Function
of Zenith AngleTitle
with Atmospheric
Correction
EOS
R0.67/R2.20
Cuiabá
Aircraft height above ground = 2.0
km
q0 = 54.1°
f = 109.3°
Zenith Angle
Michael D. King, EOS Senior Project Scientist
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July 3, 2000
Bidirectional Reflectance
Title
Measurements
EOS
 Roll: ~20°
 Time: ~2 min
 Speed: ~80 m s-1
 Height: ~600 m
 Diameter: ~3 km
 Resolution
– 10 m (nadir)
– 270 m (q = 80°)
 Channels
– 8 continuously sampled
(0.34-1.25 µm)
– 2 filter wheel channels
used for BRDF
measurements (1.64 &
2.20 µm)
Michael D. King, EOS Senior Project Scientist
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July 3, 2000
Azimuthally Averaged Reflectance Ratios
Title
R0.47/R2.20 and R0.67/R2.20 as a Function of q
EOS
R047(0..67)/R2.20
Cuiabá - BRF
Aircraft height above ground = 1.7
km
q0 = 60.4°
R0.67/R2.20
R0.47/R2.20
Zenith Angle
Michael D. King, EOS Senior Project Scientist
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July 3, 2000
Spectral Measurements of SurfaceTitle
Atmosphere Reflectance Ratios
EOS
Brasilia
Cerrad
o
R0.47/R2.20
0.0
R0.67/R2.20
0.2
Michael D. King, EOS Senior Project Scientist
0.4
R0.47/R0.67
0.6
0.8
15
1.0
July 3, 2000
Spectral Measurements of SurfaceTitle
Atmosphere Reflectance Ratios
EOS
Cuiabá
Dense
Forest
R0.47/R2.20
0.0
R0.67/R2.20
0.2
Michael D. King, EOS Senior Project Scientist
0.4
R0.47/R0.67
0.6
0.8
16
1.0
July 3, 2000
Summary and
Title
Conclusions
EOS
 For the pristine case the slopes of reflectance R0.47/R2.20 vary from
0.08–0.27 with a correlation coefficient r > 0.80 for zenith angles from
0°-65°
– For measurements taken in the forward scattering direction the
slopes < 0.1 and correlation r ~ 0.19
– For the more turbid atmosphere, ta = 0.68, the slopes R0.47/R2.20 ~
0.1 for view zenith angles 0°–40°
 Slopes of reflectance R0.67/R2.20 for the backscattering direction vary
from 0.312–0.554 for zenith angles 0°–65°
– For measurements made in the forward direction the slopes lie
between 0.233–0.473 and r < 0.80
 After the atmospheric correction is applied the slopes of reflectance
increase, with the greatest increase occurring for the largest aerosol
optical thickness
 In the case of the azimuthally averaged BRF data, the slopes increase
as a function of viewing zenith angle
– The slopes show little variation with azimuth angle, being
especially well behaved in the backward scattering directions over
dark targets
Michael D. King, EOS Senior Project Scientist
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July 3, 2000
Summary and
Title
Conclusions
EOS
 From these results a relationship between visible reflectance and
shortwave infrared reflectance exists for zenith angles from nadir to
about 40°
– However, the relationship R0.47 = 0.25 R2.20 does not seem to hold
for the cases tested here, but the relationship R0.67 = 0.5 R2.2 seems
to hold for the cases tested from 0°-45°
Michael D. King, EOS Senior Project Scientist
18
July 3, 2000