TA Calibration Bias and Trend Analysis
Chris Ruf, Amanda Mims, David ChenUniversity of Michigan
College of EngineeringDepartment of Atmospheric, Oceanic & Space Sciences
Aquarius Cal/Val Meeting15 November 2011
15 Nov. 2011 Ruf,Mims,Chen Aquarius Cal/Val pg 2
Aquarius TA Calibration
• Calibration for radiometer oceanic observations– Flags: Land fraction > 0.01%, sea ice fraction > 0.01%, TA
< 60 K or TA > 130 K, RFI contamination• Two calibration approaches
– Global average– Vicarious cold calibration
• Statistics applied over 7 days of data for stability – Centered on reported day ±3.5 days– Computed for TA observations and simulations
• Full timeseries from 29 August to 6 November, 2011
Global Average TA
15 Nov. 2011 Ruf,Mims,Chen Aquarius Cal/Val pg 3
Rad 1 (K) Rad 2 (K) Rad 3 (K)
Mean (H-pol) 88.2 82.5 76.6
Mean (V-pol) 105.6 113.2 122.0
Vicarious Cold TA
15 Nov. 2011 Ruf,Mims,Chen Aquarius Cal/Val pg 4
Rad 1 (K) Rad 2 (K) Rad 3 (K)
Mean (H-pol) 85.5 79.6 73.3
Mean (V-pol) 103.0 110.6 119.5
Observed – Expected TA
15 Nov. 2011 Ruf,Mims,Chen Aquarius Cal/Val pg 5
Pre-filtering: Ascending vs. Descending Global Averages
15 Nov. 2011 Ruf,Mims,Chen Aquarius Cal/Val pg 6
Pre-filtering: (Ascending – Descending) Global Avg. Differences
15 Nov. 2011 Ruf,Mims,Chen Aquarius Cal/Val pg 7
Pre-filtering: Ascending vs. Descending Global Averages
• (Obs–Exp) timeseries for ascending and descending passes follow same general trend, but have significant bias and trend differences
• Possible diagnostic tool for instrument errors– ND offset shouldn’t vary with pass direction– Potential to separate errors in ND and in APC
15 Nov. 2011 Ruf,Mims,Chen Aquarius Cal/Val pg 8
Pre-filtering: Northern vs. Southern Hemisphere Averages
15 Nov. 2011 Ruf,Mims,Chen Aquarius Cal/Val pg 9
Pre-filtering: Northern vs. Southern Hemisphere Ave. Differences
15 Nov. 2011 Ruf,Mims,Chen Aquarius Cal/Val pg 10
Pre-filtering: Northern vs. Southern Hemisphere Averages
• (Obs–Exp) trends between Northern and Southern hemispheric averages track relatively well but diverge over time
• Possible seasonal hemispheric imbalance in model? – Smaller hemispheric differences in Northern Fall/Southern
Spring– Now moving slowly into Northern Winter/Southern
Summer– Requires longer time series to see if trends converge again
in Northern Spring/ Southern Fall
15 Nov. 2011 Ruf,Mims,Chen Aquarius Cal/Val pg 11
Level 1A Noise Diode Ratios
• Drift analysis using internal noise diode ratios– CND: correlated noise diode– ND(DL): internal noise diode through Dicke load – ND(ANT): internal noise diode looking through antenna
• ND(DL)/CND or ND(ANT)/CND used for overall long-term drift, similar results
• Ratio of internal ND for short-term variations• Ocean-only counts from three mid-sea basins plus land, ice
and RFI flag – Land fraction > 0.01%, sea ice fraction > 0.01%, RFI contamination– Pacific: 180°W < Lon < 130°W, 30°S < Lat < 40°N– Atlantic: 55°W < Lon < 25°W, 10°N < Lat < 40°N and 30°W < Lon <
5°E, 40°W < Lat < 0°– Indian: 60°E < Lon < 90°E, 40°S < Lat < 0°
15 Nov. 2011 Ruf,Mims,Chen Aquarius Cal/Val pg 12
Noise Diode Ratios: ND(DL)/CND
15 Nov. 2011 Ruf,Mims,Chen Aquarius Cal/Val pg 13
Noise Diode Ratios: ND(ANT)/ND(DL)
15 Nov. 2011 Ruf,Mims,Chen Aquarius Cal/Val pg 14
Noise Diode Ratios: ND(DL)/ND(ANT)
15 Nov. 2011 Ruf,Mims,Chen Aquarius Cal/Val pg 15
Noise Diode Ratio Comparison
• Internal ND ratios differ from other studies (Piepmeier, 26 Oct. telecon)– Shape of variations and drift direction different for all
channels, polarizations
15 Nov. 2011 Ruf,Mims,Chen Aquarius Cal/Val pg 16
H-pol
Green: dTBDOY 2011
