Sensitivity of Off-Nadir Zenith Angles to the Surface Reflectance Ratio Technique - PowerPoint PPT Presentation

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

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Brasilia. Aircraft height above ground = 2.4 km. q0 = 45.4 f = 132.1 ... Brasilia. Cerrado. Title. Michael D. King, EOS Senior Project Scientist. July 3, 2000 ... – PowerPoint PPT presentation

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


1
Sensitivity of Off-Nadir Zenith Angles to the
Surface Reflectance Ratio Technique
  • 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.
  • 4SMA Corporation
  • Outline
  • Spectral variation of surface reflectance over
    land
  • Important for the retrieval of aerosol optical
    thickness over land

2
Goals Objectives
  • 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 065
  • Repeat for different solar zenith anglesforward
    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

3
University of Washington CV-580
4
Cloud Absorption Radiometer
  • Goddard Space Flight Center
  • developed in 1982-1983
  • University of Washington
  • integrated flown in 1984 (B-23)
  • principal data from 1987-97 (C-131A)
  • flights after 1998 (CV-580)
  • Sensor Characteristics
  • 14 spectral bands ranging from 0.34 to 2.29 µm
  • scan 95 from horizon on right-hand side of
    aircraft
  • field of view 17.5 mrad (1)
  • scan rate 1.67 Hz (100 rpm)
  • data system 9 channels _at_ 16 bit
  • 395 pixels in scan line
  • 4 reflectance calibration accuracy

5
Cloud Absorption Radiometer
Horizontal mode
Vertical mode
6
Scatter Plots of Reflectance at 0.47 and 0.67 µm
as a Function of Reflectance at 2.2 µm
Brasilia
q 30 f 132.1
q 0
Reflectance (0.47 µm 0.67 µm)
Reflectance (2.20 µm)
Reflectance (2.20 µm)
7
Reflectance Ratios R0.47/R2.20 and R0.67/R2.20 as
a Function of View Zenith Angle
Brasilia Aircraft height above ground 2.4 km q0
45.4 f 132.1
R0.47(0.67)/R2.20
R0.67/R2.20
R0.47/R2.20
Zenith Angle
8
Reflectance Ratios R0.47/R2.20 and R0.67/R2.20 as
a Function of View Zenith Angle
Reflectance Ratios R0.47/R2.20 and R0.67/R2.20 as
a Function of View Zenith Angle
Cuiabá Aircraft height above ground 2.0 km q0
54.1 f 109.3
R0.67/R2.20
R0.47(0.67)/R2.20
R0.47/R2.20
Zenith Angle
9
Reflectance Ratios R0.47/R2.20 as a Function of
Zenith Angle with Atmospheric Correction
Brasilia Aircraft height above ground 2.4 km q0
45.4 f 132.1
R0.47/R2.20
Zenith Angle
10
Reflectance Ratios R0.67/R2.20 as a Function of
Zenith Angle with Atmospheric Correction
Brasilia Aircraft height above ground 2.4 km q0
45.4 f 132.1
R0.67/R2.20
Zenith Angle
11
Reflectance Ratios R0.47/R2.20 as a Function of
Zenith Angle with Atmospheric Correction
Cuiabá Aircraft height above ground 2.0 km q0
54.1 f 109.3
R0.47/R2.20
Zenith Angle
12
Reflectance Ratios R0.67/R2.20 as a Function of
Zenith Angle with Atmospheric Correction
Cuiabá Aircraft height above ground 2.0 km q0
54.1 f 109.3
R0.67/R2.20
Zenith Angle
13
Bidirectional Reflectance Measurements
  • Roll 20
  • Time 2 min
  • Speed 80 m s-1
  • Height 600 m
  • Diameter 3 km
  • Resolution
  • 10 m (nadir)
  • 270 m (? 80)
  • Channels
  • 8 continuously sampled (0.34-1.25 µm)
  • 2 filter wheel channels used for BRDF
    measurements (1.64 2.20 µm)

14
Azimuthally Averaged Reflectance Ratios
R0.47/R2.20 and R0.67/R2.20 as a Function of q
Cuiabá - BRF Aircraft height above ground 1.7
km q0 60.4
R0.67/R2.20
R047(0..67)/R2.20
R0.47/R2.20
Zenith Angle
15
Spectral Measurements of Surface-Atmosphere
Reflectance Ratios
Brasilia Cerrado
R0.47/R2.20
R0.47/R0.67
R0.67/R2.20
0.0 0.2 0.4
0.6 0.8 1.0
16
Spectral Measurements of Surface-Atmosphere
Reflectance Ratios
Cuiabá Dense Forest
R0.47/R2.20
R0.47/R0.67
R0.67/R2.20
0.0 0.2 0.4
0.6 0.8 1.0
17
Summary and Conclusions
  • For the pristine case the slopes of reflectance
    R0.47/R2.20 vary from 0.080.27 with a
    correlation coefficient r gt 0.80 for zenith
    angles from 0-65
  • For measurements taken in the forward scattering
    direction the slopes lt 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
    040
  • Slopes of reflectance R0.67/R2.20 for the
    backscattering direction vary from 0.3120.554
    for zenith angles 065
  • For measurements made in the forward direction
    the slopes lie between 0.2330.473 and r lt 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

18
Summary and Conclusions
  • 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
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