Long_OVWST2011_OSCAT_final

advertisement
Initial Results on the CrossCalibration of QuikSCAT and
Oceansat-2 Scatterometers
David G. Long
Department of Electrical and Computer Engineering
Brigham Young University
May 2011
QuikSCAT vs OSCAT
Parameter
QuikSCAT
OceanSat-2 Scatterometer
Sponsoring Organization
NASA/JPL
ISRO
Operational Frequency
13.402 GHz
13.515 GHz
Polarization (Inner/Outer)
HH/VV
HH/VV
Antenna Diameter
1m
1m
Altitude at Equator
803 km
720 km
Orbit Near Repeat Cycle
4 days
2 days
Local time at asc/desc node
6:00 a.m. at asc node
noon at desc node
HH 3dB footprint (Az x El)
24 x 31 km
26.8 x 45.1 km
VV 3 dB footprint (Az x El)
26 x 36 km
29.7 x 68.5 km
Incidence Angle (Inner)
46 deg
49 deg
Incidence Angle (Outer)
54 deg
57 deg
Swath Diameter (Inner)
1400 km
1400 km
Swath Diameter (Outer)
1800 km
1836 km
Pointing Accuracy
+/- 0.05 deg
+/- 0.15 deg
Elevation Pointing (w/ attitude error)
+/- 0.05 deg
+/- 0.25 deg
Begin / End Date
201-1999/ 327-2009
309-2009/ present
DGL May 2011
2
OSCAT & QuikSCAT Hi Res
QuikSCAT
GRD
OSCAT
GRD
QuikSCAT
SIR
OSCAT
SIR
•QuikSCAT and
OceanSat-2
Scatterometer
(OSCAT) have
comparable
spatial sampling
and resolution
•Similar image
enhancement
possible
– Can use
QuikSCAT
algorithms for
OSCAT
DGL May 2011
3
Conventional resolution 25 km/pixel
JD 309, 2009
DGL May 2011
* Preliminary 2.225 km/pixel
Enhanced Resolution*
OSCAT Image
4
QuikSCAT/OSCAT Image Comparison
OSCAT H
OSCAT V
QuikSCAT H
QuikSCAT V
• Comparison of one day
BYU backscatter images
– OSCAT and QuikSCAT
have nearly identical
characteristics
– Differences due to
azimuth and local time of
day
– Similar variances and
means
– Similar spatial
enhancement possible
• OSCAT can contribute to
the multi-decade
scatterometer climate
record of land and ice
observations
DGL May 2011
5
OSCAT/QuikSCAT Differences for the
Land/Ice Scatterometer Climate Record
• Nominal incidence angle differs
– H: QuikSCAT=46°, OSCAT=48°
– V: QuikSCAT=54°, OSCAT=56°
• Orbit geometry differs
– OSCAT has better coverage near poles (smaller holes)
– Time of orbit ascending node differ
• QuikSCAT=6:30 am OSCAT=noon
• Local time of measurements vary (location dependent)
– Orbit revisit time (Q=4 day repeat, O=2 day repeat)
– Azimuth angle distributions differ and vary
• Need to apply azimuth angle corrections
• Improved sigma-0 cross-calibration needed
DGL May 2011
6
Linear model for sigma-0 vs incidence angle
• Simplified model
• Can also use for egg/slice incidence angle correction
(dB)
(dB)
ASCAT Amazon Rain Forest Example
ASCAT
DGL May 2011
ASCAT
7
Backscatter Anisotropy
• Due to sastrugi and topography, some polar regions exhibit
anisotropic backscatter response
- Differences in azimuth geometry can be confused with
climate changes if not accounted for
• Do not expect azimuth variations over the Amazon
ASCAT Wilkes Land Example
ASCAT (C-Band) V-pol
(dB)
40 inc
ASCAT (C-Band)
DGL May 2011
8
QuikSCAT Anisotropy
• QuikSCAT has fixed incidence
angles but high diversity in
azimuth angle observations
54 inc
– Similar anisotropy observed
QuikSCAT V-pol (Ku-Band)
46 inc
QuikSCAT (Ku-Band)
DGL May 2011
QuikSCAT H-pol (Ku-Band)
9
QuikSCAT / ASCAT Comparison
• Different frequencies (5.4 GHz vs 13.5 GHz) and
incidence angles (40 V vs 46 H & 54 V)
– Consistent with dominant sastrugi scattering
DGL May 2011
10
OSCAT Azimuth Modulation Analysis
OSCAT 310-311, 2009
OSCAT slice measurements: 13,099
QuikSCAT slice measurements: 14,118
DGL May 2011
Locations of OSCAT
sigma-0 measurements
within study region
JD 309-327, 2009
11
Slice Sigma-0 vs Azimuth Angle
DGL May 2011
12
Azimuth Corrected
Slice Sigma-0 vs Azimuth Angle
DGL May 2011
13
Comparison of OSCAT and QuikSCAT
modulation for the study region
• OSCAT azimuth modulation does not match
QuikSCAT azimuth modulation
– Improved processing is expected to resolve this
H-pol
V-pol
OSCAT
QuikSCAT
DGL May 2011
14
OSCAT Slice Sigma-0 vs Incidence Angle
DGL May 2011
(narrow incidence angle range)
15
Azimuth Corrected Slice Sigma-0 vs Incidence Angle
DGL May 2011
16
Comparison of Sigma-0 Distributions
in the Antarctic Study Region
H-pol bias 0.7 dB
V-pol bias 0.0 dB
DGL May 2011
17
Comparison of Azimuth Corrected Sigma-0 Distributions
in the Antarctic Test Region
H-pol bias 0.6 dB
V-pol bias 0.2 dB
DGL May 2011
18
Amazon Study Region
• Rain forest is a good
calibration target
(anisotropic), but exhibits
spatial inhomogeneity
– Select homogenous
region
• Time-of-day variation
– Sigma-0 varies with time
of day as moisture moves
up/down in canopy
– Several tenths of a dB
effect
• OSCAT and QuikSCAT
observe at different local
times
– No azimuth variation
expected
Select region that both QuikSCAT and
OSCAT sigma-0 fall within narrow range
• Different incidence angles
– Small mean differences
DGL May 2011
19
Egg Sigma-0 vs Incidence Angle
DGL May 2011
20
Incidence-Corrected Egg Sigma-0 vs Incidence Angle
DGL May 2011
21
Egg Sigma-0 vs Azimuth Angle
DGL May 2011
22
Azimuth-Corrected Egg Sigma-0 vs Azimuth Angle
DGL May 2011
23
Comparison of Egg Sigma-0 distribution in
Amazon Study Region
H-pol bias 0.05 dB
V-pol bias 0.25 dB
DGL May 2011
24
Comparison of Corrected Sigma-0 Distribution
in Amazon Study Region
H-pol bias 0 dB
V-pol bias 0.25 dB
DGL May 2011
25
OSCAT Local Time of Day Analysis
DGL May 2011
Time in minutes from start
26
OSCAT Local Time of Day Analysis
Arctic
Antarctic
Equi-latitude strips used for measurement extraction in LTD analysis
superimposed upon OSCAT gridded sigma-0 images of the polar regions
DGL May 2011
27
Comparison of Northern Hemisphere
Local Time of Day Observations
OSCAT
SeaWinds
QuikSCAT
LTD (hours) = UTC + Local_Longitude / 15
Scatterplot of LTD vs UTC in the Northern Hemisphere for different
longitude bins (a) OSCAT, (b) Seawinds, (c) QuikSCAT
DGL May 2011
28
Comparison of Southern Hemisphere
Local Time of Day Observations
OSCAT
SeaWinds
QuikSCAT
LTD (hours) = UTC + Local_Longitude / 15
Scatterplot of LTD vs UTC in the Southern Hemisphere for different
longitude bins (a) OSCAT, (b) Seawinds, (c) QuikSCAT
DGL May 2011
29
Diagram of LTD Divisions for Four
Scatterometers
LTD (hrs) = UTC + Local_Longitude / 15
24 hours
DGL May 2011
24 hours
30
Conclusion
• QuikSCAT and OSCAT sensors very similar
– Calibrated OSCAT products will be similar to QuikSCAT products
• Validated QuikSCAT land/ice SCP products
– Daily Antarctic iceberg products (operational)
– Daily sea ice extent and mapping (operational, widely distributed)
– Daily FY/MY ice classification (relatively new)
• Can be averaged to longer time scales
• Post wind mission (PWM) QuikSCAT data supports OSCAT
calibration
– PWM QuikSCAT Coverage is too limited for less than monthly maps,
aliasing an issue for ice movement for monthly maps
DGL May 2011
31
Download
Related flashcards
Create Flashcards