Ocean Surface Topography Calibration and Performance Assessment of the JMR and TMR Shannon Brown, Shailen Desai, Wenwen Lu NASA Jet Propulsion Laboratory

Brown et al. OSTST07-Hobart JMR Calibration Status Most recent calibration on JMR version B GDR No large calibration offsets observed after Nov safehold Slight change in 23.8 GHz ND 1 observed, should have < 2mm effect on PDs Cause of the JMR PD scale error reported at Venice SWT was identified and corrected –This will be implemented in the version-C GDRs –Users can apply ad-hoc correction by dividing PDs by 1.023

Brown et al. OSTST07-Hobart TMR Calibration Status End-of-mission GDR calibration effort completed TMR replacement product is available Details of the calibration methodology and results are presented here (and in poster in C/V room)

Brown et al. OSTST07-Hobart On-Earth T B References Tune radiometer to on-Earth hot and cold T B references –Vicarious Cold Reference (Ruf, 2000, TGARS) Stable, statistical lower bound on ocean surface brightness temperature –Amazon pseudo-blackbody regions (Brown and Ruf, 2005, JTECH) T HOT (frequency, incidence angle, Local Time, Time of year) SSM/I 37.0 GHz V-pol – H-pol TB Histogram of Cold T B s Hot Reference Regions

Brown et al. OSTST07-Hobart Sensitivity of References to Climate Variability Cold reference –Small annual signal present (~ K peak to peak) –Stable over many years? Hot reference –Significant diurnal (~6K) and annual (~2K) signal present –Minimum annual signal in early morning hours –Affected by El Nino/La Nina Observed TMR 18.0 GHz Amazon TBsObserved TMR 21.0 GHz Cold Reference Annual harmonic fit + linear drift

Brown et al. OSTST07-Hobart Hot Reference Model Use NCEP/NCAR Reanalysis-1 4x-daily fields to model Amazon regions –Surface emissivity estimated from SSM/I for each TMR frequency –NCEP provides temperature, pressure and humidity for radiative transfer –4-x daily modeled T B s are interpolated to TMR observation times –Model is able to replicate the observations during 1997/98 El Nino Observed TMR 18.0 GHz Amazon TBs Modeled 18.0 GHz Amazon TBs *NCEP Reanalysis data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their Web site at

Brown et al. OSTST07-Hobart Cold Reference Stability SST, PWV and TB joint statistics computed using NCEP/NCAR Re- analysis 4x-daily fields for GHz21.0 GHz37.0 GHz PWV SST

Brown et al. OSTST07-Hobart Cold Reference Stability Cold reference TB for each channel is sensitive to different areas of joint probability distribution of SST and water vapor 18.0 GHz 21.0 GHz 37.0 GHz

Brown et al. OSTST07-Hobart Sensitivity of Cold Reference SST/PWV joint probability distribution is artificially perturbed to assess impact on cold reference No significant changes in cold reference until probability of occurrence in optimum SST/PWV regions decreases by about 40% Contend that cold reference is stable over TMR lifetime and any drifts are related to calibration errors 21.0 GHz Cold Reference Deviation 37.0 GHz Cold Reference Deviation

Brown et al. OSTST07-Hobart TMR T B Drift Known 1.5 K drift in TMR 18.0 GHz channel, attributed to drift in cold sky horn switch isolation (Ruf, 2002 TGARS) Small drifts also observed in 21.0 and 37.0 GHz cold TBs <0.5 K over 13 years 0.5 K drift observed in 37.0 GHz hot TB, little drift observed in 18.0 and 21.0 GHz hot TB Gain and offset errors observed TMR - Cold Reference [K]TMR - Hot Reference [K]

Brown et al. OSTST07-Hobart Instrument Temperature (Yaw State) Dependency Sample on-Earth references w.r.t. instrument temperature Temperature dependency as high as 0.7 K peak-to-peak at cold end ChanneldT COLD /dT Inst dT HOT /dT Instf 18.0 GHz0.049 K/K0.036 K/K 21.0 GHz K/K0.059 K/K 37.0 GHz0.022 K/K0.084 K/K RaOb-TMR PD vs Instrument Temperature dPD/dT = 0.36 mm/K dPD/dT = 6e-5 mm/K Recalibrated TMR GDR TMR ChanneldT COLD /dT Inst dT HOT /dT Inst 18.0 GHz K/K-5e-4 K/K 21.0 GHz K/K K/K 37.0 GHz K/K0.017 K/K Recalibration reduces instrument temperature dependence to < 0.1 K peak-to-peak at cold end

Brown et al. OSTST07-Hobart TMR PDs compared to SSM/I Recalibrated PD drift compared to SSM/I derived PDs is reduced to mm/yr over 13 years Validates that cold reference is stable over this time period Minimization of yaw state errors evident in reduced noise (std. dev. of difference is 1.1 mm for TMR recal.) *SSM/I vapor fields acquired from Remote Sensing Systems SSM/I – TMR PD Recalibrated TMR

Brown et al. OSTST07-Hobart Path Delay Validation TMR PD vs RaOb PD During the initial TMR post-launch cal/val, the PD coefficients were increased by ~5% to remove a PD scale error –This was attributed to the model for the water vapor absorption line strength being too low The PD coefficient scaling was compensating for the large gain errors in the T B s After correcting the gain errors in the T B s, a 5% scale error became evident in the PDs This was removed by reverting to the pre-launch TMR PD coefficients *

Brown et al. OSTST07-Hobart Comparisons to JMR JMR PD coefficients also require adjustment to account for spurious increase in water vapor absorption model line strength After JMR PD coefficient adjustment, scale error is negligible between JMR and TMR Additionally, scale error in JMR compared to ECMWF and GPS, which was reported at the Venice SWT, is removed with PD coefficient adjustment Additional details in presentation by S. Desai

Brown et al. OSTST07-Hobart Cycles 1-21 JMR – TMR Regional Biases on 0.4 o x0.4 o grid dPD [mm]

Brown et al. OSTST07-Hobart JMR-TMR Regional Error Statistics Averaged JMR/TMR differences on a 0.4 o lat/lon grid for cycles 1-21 Nearly half of the averages have differences of < 1 mm 90 % have differences of < 3 mm

Brown et al. OSTST07-Hobart Summary TMR recalibration is complete T B drifts, gain and offset errors, and instrument temperature dependent errors were removed PD coefficients were reverted to pre-launch values TMR PDs are in good agreement with several validation sources –No drift compared to SSM/I –Low bias and negligible scale error compared to RaOb, GPS, and ECMWF After JMR PD coefficient adjustment, TMR and JMR are in excellent agreement –Although, there is still room for regional improvement –JMR calibration will be updated on version-C GDRs

Brown et al. OSTST07-Hobart TMR Climate Record

Brown et al. OSTST07-Hobart Backup

TMR Vapor Trends Work is on-going to produce climatology from TMR data Stevens (1990) derives approximate mean relationship between integrated vapor and SST Differentiating gives â = 0.05, R 2 =0.46: all SST â = 0.06, R 2 =0.36: SST > 15 o C