Date post: | 13-Jan-2016 |
Category: |
Documents |
Upload: | lydia-hall |
View: | 220 times |
Download: | 0 times |
Calibration and Validation Studies for Aquarius Salinity Retrieval
PI: Shannon BrownCo-Is: Shailen Desai and Anthony Scodary
Jet Propulsion Laboratory, California Institute of Technology
Project Objectives
• Perform a rigorous on-orbit calibration of the Aquarius and MWR radiometers and retrieval validation– Our objective is to identify the cause of any observed calibration or
retrieval error or instability in order to apply a suitable correction at the appropriate level of processing
– Ensures well calibrated brightness temperatures for other applications (e.g. soil moisture)
– Follows approach developed for altimeter radiometers (Topex, Jason)
• Develop an empirical L-band rough sea surface emission model
• Develop a sea surface roughness correction algorithm to improve salinity retrieval
• Analyses will begin with SMOS data
Calibration Approach for Aquarius and MWR
-8
-4
0
4
8
12
16
20
0 20 40 60 80 100 120 140 160
JMR(VA)-GPSJMR(VA)-SSMIJMR(VA)-TMIJMR(VA)-Model
Jason Repeat Cycle
Cycle 31
Cycle 68
Monitor instrument level parameters and diagnostics
Compare brightness temperatures to natural on-Earth reference targets
Compare retrievals to in
situ ground truth or models
Instrument Level Monitoring
• Track metrics of instrument stability to detect and diagnose calibration anomalies – relative noise diode ratios
– reference load counts
– receiver gain
– relative brightness temperature stability between the different polarizations and feed horns
• Plots continuously updated and viewable via a web interface
AMR 34-18.7 GHz Ocean TBs
AMR 34-18.7 GHz Land TBs
Discontinuities indicate calibration
shifts
AMR 18.7 GHz ND Ratios
AMR 18.7 GHz Gain
Developing On-Earth TB Calibration References at L-band
• Assess natural targets for L-band radiometer calibration over on-Earth dynamic range– Calm, flat ocean scenes
– Land areas: flat, dry deserts; homogeneous heavily vegetated regions
– Ice sheets: Antarctica (e.g. Dome-C), Greenland
• Use to assess absolute calibration, monitor stability and assess residual instrument calibration errors
Compare over time
Compare versus instrument front end temperature
37 V-H
23 V-H
18 V-H
10 V-H
6 V-H
AMSR-E De-polarization
Salinity Retrieval Validation
• Form database of Aquarius co-locations with in situ data– Argo float array, the Shipboard Sensor Database
(SSD) and the Global Temperature-Salinity Profile Program (GTSPP).
• Analyze global mean differences between Aquarius retrieved salinity and in-situ measurements – Assess over time and instrument temperature
• Analyze regional differences– Assess antenna pattern correction, faraday
rotation correction and atmospheric and roughness corrections
6
Ocean Rough Surface Emission Model
• Develop empirical rough surface emission/backscatter model– Function of significant wave height and surface wind speed
• Form co-located database of SMOS/Aquarius TB data and Aquarius σ0 with satellite altimeter derived SWH and WS and in situ SST and SSS measurements– Remove atmospheric contribution to determine emissivity, sigma0
– Evaluate model function for emissivity and sigma0 both globally and regionally
Significant Wave Height Surface Wind Speed
Plots from Aviso: Topex/Poseidon data
Roughness Correction Algorithm
• Accurate roughness correction algorithm is vital to ensure high-quality salinity retrievals
• Explore two types of algorithms
– Characterize σ0 to excess TB relationship for different regions classified by the statistics of the sea state.
– Algorithms that directly use ancillary wind speed and significant wave height data as inputs
• Algorithm types– Radar backscatter only
– Radar backscatter and ancillary surface wind speed
– Radar backscatter and ancillary significant wave height
– Radar backscatter, wind speed and wave height
– Only wind speed and wave height 8
• Match-ups distributed over global oceans (+/- 66 degrees)
• Significant number of match-ups with minimal temporal and spatial difference– ~170,000 match-ups per horn
for 28-day simulation9
Match-ups With Simulated Data
Number of match-ups per 1o bin – all horns
Faraday Rotation Correction
• Dual-frequency altimeter match-ups also useful for assessing Faraday rotation correction
• Match-ups cover large range of TEC values
10
Summary
• We will perform studies to assess the calibration of the Aquarius and MWR radiometers and validate the retrievals
• Develop an empirical L-band rough surface emission model and use it to develop roughness correction algorithms
11