Aquarius Sca+erometer Calibra3on Fore, A., Neumann, G., Freedman, A., Chaubell, M., Tang, W., Hayashi, A., and Yueh, S. 217 California Ins3tute of Technology, Government Sponsorship acknowledged
Aquarius Instrument Calibra3on Aquarius includes a loop back calibra3on feature Tracks transmit power and receiver gain product. Any varia3ons within the loop back pathway are automa3cally corrected in σ computa3on. Some key por3ons of hardware lie outside of loopback pathway These are controlled thermally to ~.5 deg C temperature varia3ons. Or designed to be insensi3ve to changing temperature.
3.75 Scatterometer Loop back Power 3.775 3.8 Power [dbm] 3.825 3.85 3.875 Order.1 db changes in loop-back power over mission 3.9 Beam 1 HV Beam 1 VV 3.925 Beam 1 VH Beam 1 HH 3.95 9/11 1/12 6/12 11/12 4/13 9/13 2/14 7/14 12/14 5/15
Key Scatterometer Component Temperatures outside of Loop back 22 Step Attenuator 21.5 Loop back Attenuator Loop back Switch Beam Switch 21 Temperature [deg C] 2.5 2 19.5 19 18.5 18 9/11 1/12 6/12 11/12 4/13 9/13 2/14 7/14 12/14 5/15
67.5 CND Gain Estimated On V Receive Beam 1 CND Gain 67.45 Gain [db] 67.4 67.35 Es3mate receiver gain using difference of adjacent noise power observa3ons with and without the known CND power 67.3 67.25 9/11 1/12 6/12 11/12 4/13 9/13 2/14 7/14 12/14 5/15
Gain Ratio [db] 71.19 71.2 71.21 71.22 71.23 71.24 Ratio of Loop back Power to CND Gain Beam 1 Loop back / CND Gain Ratio Differences between loop-back and CND gain due to -cabling between CND and loopback path (can effect σ ) -changes in CND power (no effect on σ ) -changes in TX power (no effect on σ ) Max effect on σ of ~.1 db if due to cabling (twice observed difference) 71.25 71.26 9/11 1/12 6/12 11/12 4/13 9/13 2/14 7/14 12/14 5/15
.5 Delta Sigma HH [db].25.25.5.75.1.125.15.175.2 Order.1 db changes in measured expected σ over mission (without dri] correc3on) Beam 1 Beam 2 Beam 3 Dec 11 Jun 12 Dec 12 Jun 13 Dec 13 Jun 14 Dec 14
.5 Delta Sigma VV [db].25.25.5.75.1.125.15.175.2 Order.1 db changes in measured expected σ over mission (without dri] correc3on) Beam 1 Beam 2 Beam 3 Dec 11 Jun 12 Dec 12 Jun 13 Dec 13 Jun 14 Dec 14
Amazon γ γ = σ cos ( θinc ) PALSAR found γ values in the Amazon stable across 2-45 degrees in incidence angle* Wet-dry seasonal difference of ~.27 db** Wet season is approx. Nov-April. Best es3mates are: HH ~ -6.28 db (std.18) HV ~ -11.15 db (std.21) Does not have RAP correc3on *M. Shimada, O. Isoguchi, T. Tadono, and K. Isono. Palsar radiometric and geometric calibra3on. Geoscience and Remote Sensing, IEEE Transac3ons on, 47(12):3915 3932, dec. 29 (Images from this source) **M. Shimada. Long-term stability of l-band normalized radar cross sec3on of amazon rainforest using the jers-1 sar. Canadian Journal of Remote Sensing, 31(1): 132 137, 25. RAP correc3on is range antenna pa+ern correc3on Has RAP correc3on
Regions used in γ Analysis Include data in blue polygon that not in black polygon 5 3 1 1 Latitude 3 5 7 9 11 13 15 75 73 71 69 67 65 63 61 59 57 55 53 51 Longitude
5.75 6 6.25 6.5 6.75 5.75 6 6.25 6.5 6.75 1.5 1.75 11 11.25 11.5 Amazon Gamma HH [db] Amazon Gamma VV [db] Amazon Gamma HV [db] Oct 11 May 12 Nov 12 Jun 13 Jan 14 Jul 14 Feb 15 Beam 1 Beam 2 Beam 3
Bias compared to PALSAR PALSAR values: HH: -6.28 db; HV: -11.15 db Asc / Dec Beam 1 Beam 2 Beam 3 All HH.2.8.12 Ascending HH.4.7.6 Descending HH -.1.9.2 All VV -.4.6.7 Ascending VV -.2.4.6 Descending VV -.5.7.9 All HV.6.21.13 Ascending HV.8.19.9 Descending HV.5.22.19 No significant ascending / descending difference
Ocean Comparison Aquarius HH / PALSAR HH Plot of PALSAR HH GMF (black square) and our Aquarius HH GMF ( red o). -Compute wind speed PDF weighted mean ra3o of Aquarius GMF divided by PALSAR GMF. Beam 1 2 3 Mean Ra3o [db].55.1 -.71 A [db] 5 1 15 2 Beam 1; Aquarius vs PALSAR A; Mean Ratio [db]:.55 Aquarius PALSAR 25 2.5 5 7.5 1 12.5 15 17.5 2 22.5 25 Wind Speed [m/s] 1 Beam 2; Aquarius vs PALSAR A; Mean Ratio [db]:.1 15 Beam 3; Aquarius vs PALSAR A; Mean Ratio [db]:.71 12 14 16 2 A [db] 18 2 22 24 26 28 Aquarius PALSAR 3 2.5 5 7.5 1 12.5 15 17.5 2 22.5 25 Wind Speed [m/s] A [db] 25 3 Aquarius PALSAR 35 2.5 5 7.5 1 12.5 15 17.5 2 22.5 25 Wind Speed [m/s]
4 Bias STD SCAT Speed compared to SSMI/S SCAT Speed Bias / STD [m/s] 3 2 1 Overall Bias:.35 Overall STD: 1.15 1 2.5 5 7.5 1 12.5 15 17.5 2 22.5 25 SSMI/S Speed [m/s]
4 Bias STD CAP Speed compared to SSMI/S CAP Speed Bias / STD [m/s] 3 2 1 Overall Bias:.165 Overall STD: 1.46 1 2.5 5 7.5 1 12.5 15 17.5 2 22.5 25 SSMI/S Speed [m/s]
Triple-Colloca3on Results The sca+erometer-only wind speed product has performance within.2 m/s RMS of RapidSCAT Bias Slope RMS Error SSMI 1.667 RapidScat.444.9525.7333 SCAT 4. -.1193 1.184.9531 Bias Slope RMS Error SSMI 1.6715 RapidScat.4395.9532.7295 CAP 4. -.3214 1.752.8953
Triple-Colloca3on Results (u/v component) The vector triple-colloca3on results suggest that the CAP wind direc3on is not as good as that from RapidScat. U Component Bias Slope RMS Error ECMWF 1.817 RapidScat -.997.9912 1.1487 CAP 4. -.273 1.39 1.3924 V Component Bias Slope RMS Error ECMWF 1.8187 RapidScat.427 1.265 1.4584 CAP 4. -.35 1.383 1.5944
Wind Speed Bias/STD as compared to SSMI/S 1.2 Bias/STD [m/s] 1.8.6.4 Scat Bias Scat STD CAP Bias CAP STD.2.2 211 212 213 214 215 216
Summary Aquarius is a stable source of calibrated L-band backsca+er over the mission. Stability: Instrument only predicts worst-case of.1 db Measured model shows order.1 db dri] corrected for in V4. data Aquarius is calibrated to be consistent with PALSAR Amazon: We find no significant ascending descending difference. Seasonal varia3on of.5 db over Amazon. Ocean: Comparison of Aquarius and PALSAR model func3ons shows they are calibrated to the 1 db level. Various factors can explain the residual differences (ancillary wind speed used, etc.). Aquarius has been used as reference for SMAP radar calibra3on. Aquarius provides a wind speed product with accuracy approaching that from previous Ku and C-band sca+erometers.
Backups
3 27 Histogram of SCAT vs SSMI/S Speed 11 1 24 9 SCAT Speed [m/s] 21 18 15 12 9 8 7 6 5 4 3 Log(Counts) 6 2 3 1 3 6 9 12 15 18 21 24 27 3 SSMI/S Speed [m/s]
3 27 Histogram of CAP vs SSMI/S Speed 11 1 24 9 CAP Speed [m/s] 21 18 15 12 9 8 7 6 5 4 3 Log(Counts) 6 2 3 1 3 6 9 12 15 18 21 24 27 3 SSMI/S Speed [m/s]
PALSAR Found γ HH = -6.28 db and γ HV = -11.15 db Histograms of Aquarius γ For the Three Beams 15 B1; Mean HH gamma: 6.28 4 B2; Mean HH gamma: 6.28 15 B3; Mean HH gamma: 6.23 1 5 3 2 1 1 5 7.5 7 6.5 6 5.5 5 B1; Mean VV gamma: 6.33 15 1 5 7.5 7 6.5 6 5.5 5 B1; Mean HV gamma: 11.11 15 7.5 7 6.5 6 5.5 5 B2; Mean VV gamma: 6.27 4 3 2 1 7.5 7 6.5 6 5.5 5 B2; Mean HV gamma: 11.1 6 7.5 7 6.5 6 5.5 5 B3; Mean VV gamma: 6.24 15 1 5 7.5 7 6.5 6 5.5 5 B3; Mean HV gamma: 11.8 15 1 4 1 5 2 5 12.5 12 11.5 11 1.5 1 12.5 12 11.5 11 1.5 1 12.5 12 11.5 11 1.5 1