Aquarius Sca+erometer Calibra3on

Transcription

1 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

2 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 3.75 Scatterometer Loop back Power Power [dbm] Order.1 db changes in loop-back power over mission 3.9 Beam 1 HV Beam 1 VV Beam 1 VH Beam 1 HH /11 1/12 6/12 11/12 4/13 9/13 2/14 7/14 12/14 5/15

4 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] /11 1/12 6/12 11/12 4/13 9/13 2/14 7/14 12/14 5/15

5 67.5 CND Gain Estimated On V Receive Beam 1 CND Gain Gain [db] Es3mate receiver gain using difference of adjacent noise power observa3ons with and without the known CND power /11 1/12 6/12 11/12 4/13 9/13 2/14 7/14 12/14 5/15

6 Gain Ratio [db] 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) /11 1/12 6/12 11/12 4/13 9/13 2/14 7/14 12/14 5/15

7 .5 Delta Sigma HH [db] 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

8 .5 Delta Sigma VV [db] 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

9 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 ~ db (std.18) HV ~ 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): , 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): , 25. RAP correc3on is range antenna pa+ern correc3on Has RAP correc3on

10 Regions used in γ Analysis Include data in blue polygon that not in black polygon Latitude Longitude

11 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

12 Bias compared to PALSAR PALSAR values: HH: db; HV: db Asc / Dec Beam 1 Beam 2 Beam 3 All HH Ascending HH Descending HH All VV Ascending VV Descending VV All HV Ascending HV Descending HV No significant ascending / descending difference

13 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 Mean Ra3o [db] A [db] Beam 1; Aquarius vs PALSAR A; Mean Ratio [db]:.55 Aquarius PALSAR 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]: A [db] Aquarius PALSAR Wind Speed [m/s] A [db] 25 3 Aquarius PALSAR Wind Speed [m/s]

14 4 Bias STD SCAT Speed compared to SSMI/S SCAT Speed Bias / STD [m/s] Overall Bias:.35 Overall STD: SSMI/S Speed [m/s]

15 4 Bias STD CAP Speed compared to SSMI/S CAP Speed Bias / STD [m/s] Overall Bias:.165 Overall STD: SSMI/S Speed [m/s]

16 Triple-Colloca3on Results The sca+erometer-only wind speed product has performance within.2 m/s RMS of RapidSCAT Bias Slope RMS Error SSMI RapidScat SCAT Bias Slope RMS Error SSMI RapidScat CAP

17 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 RapidScat CAP V Component Bias Slope RMS Error ECMWF RapidScat CAP

18 Wind Speed Bias/STD as compared to SSMI/S 1.2 Bias/STD [m/s] Scat Bias Scat STD CAP Bias CAP STD

19 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.

20 Backups

21 3 27 Histogram of SCAT vs SSMI/S Speed SCAT Speed [m/s] Log(Counts) SSMI/S Speed [m/s]

22 3 27 Histogram of CAP vs SSMI/S Speed CAP Speed [m/s] Log(Counts) SSMI/S Speed [m/s]

23 PALSAR Found γ HH = db and γ HV = db Histograms of Aquarius γ For the Three Beams 15 B1; Mean HH gamma: B2; Mean HH gamma: B3; Mean HH gamma: B1; Mean VV gamma: B1; Mean HV gamma: B2; Mean VV gamma: B2; Mean HV gamma: B3; Mean VV gamma: B3; Mean HV gamma: