Joint GRWG and GDWG Meeting 09-11 February 2010, Toulouse, France Monitoring of IR Clear-sky Radiances over Oceans for SST (MICROS) Towards Cross-Platform Radiance Consistency Between AVHRRs Onboard NOAA-16, -17, -18, -19 and MetOp-A Alexander Ignatov and XingMing Liang NOAA/NESDIS, Center for Satellite Applications and Research Alex.Ignatov@noaa.gov and XingMing.Liang@noaa.gov Presented by: Andy Heidinger NESDIS/STAR and U. Wisconsin 10 February 2010 Joint GRWG & GDWG Meeting Toulouse, France

Joint GRWG & GDWG Meeting Toulouse, France MICROS A web-based Near-Real Time tool http://www.star.nesdis.noaa.gov/sod/sst/micros/ Monitoring global “model minus observation” bias Model: Community Radiative Transfer Model (CRTM) used in conjunction with GFS upper air data and Reynolds SST Observation*: AVHRR Ch3B (3.7μm), Ch4(11μm), and Ch5(12μm) onboard NOAA-16, -17, -18, -19 and MetOp-A Implemented in July 2008 *Produced by the Advanced Clear-Sky Processor over Oceans (ACSPO) 10 February 2010 Joint GRWG & GDWG Meeting Toulouse, France

Joint GRWG & GDWG Meeting Toulouse, France Objectives MICROS Objectives Monitor and test improvements in ACSPO main product - Clear-Sky Radiances over Oceans Validate and improve Community Radiative Transfer Model (CRTM) Monitor AVHRR radiances over clear-sky global ocean in NRT for stability, self- and cross-platform consistency This presentation: Present examples of nighttime analysis in Ch3b (3.7 μm) Discuss potential factors affecting cross-platform consistency CRTM v1 performance during daytime suboptimal & being improved 10 February 2010 Joint GRWG & GDWG Meeting Toulouse, France

Joint GRWG & GDWG Meeting Toulouse, France Methodology Use robust statistics to monitor brightness temperatures (BT) More informative of sensor calibration performance (Minimizes effects of possible outliers) Employ Double-differencing (DD) technique to rectify cross-platform biases from “noise” in M-O bias NOAA-17 = Reference satellite (Stable; EXT close to MetOp-A) CRTM used as a ‘transfer standard’ DD minimizes artifacts in M-O biases arising from e.g. Errors in Reynolds SST and GFS upper air data Missing aerosol in current implementation Possible systematic biases in CRTM Changing versions of ACSPO algorithm Note that DD do take into account differences in spectral responses between different sensors (unless those are in error) 10 February 2010 Joint GRWG & GDWG Meeting Toulouse, France

Nighttime M-O bias in Ch3b: Maps NOAA-19, 28 March 2009, 00-24 UTC Close to zero and uniformly distributed 10 February 2010 Joint GRWG & GDWG Meeting Toulouse, France

Nighttime M-O bias in Ch3b: Histograms NOAA-16, -17, 18, 19, and MetOp-A 28 March 2009 Model is warmer than Obs by ~0.1 K due to using bulk SST (instead of skin) using diurnal-mean Reynolds SST at night missing aerosol in CRTM implementation possible residual cloud in AVHRR BTs Stat: 2.5-3 million clear-sky pixels per day Shape of histograms: Close to Gaussian Cross-platform consistency: within ~0.1 K (Note: Overpass time is from 9:30pm-5am) 10 February 2010 Joint GRWG & GDWG Meeting Toulouse, France

Nighttime M-O bias in Ch3b: Angular Dependencies NOAA-16, -17, 18, 19, and MetOp-A 28 March 2009 Angular dependencies: within <0.2 K Cross-platform consistency: within < 0.1 K 10 February 2010 Joint GRWG & GDWG Meeting Toulouse, France

Joint GRWG & GDWG Meeting Toulouse, France Stability of biases in Ch3b BT and SST V1.02 V1.10 V1.00 BT Biases in Ch3b ACSPO version: No effect on M-O biases SST Biases (Retrieved – Reynolds) BT and SST biases change in time by several tenths of a Kelvin. BT bias change in anti-phase with SST biases. This suggests that Reynolds SST (input to CRTM) is unstable within several tenths of a Kelvin. 10 February 2010 Joint GRWG & GDWG Meeting Toulouse, France

Double Differences (DD) in Ch3b: Cancel out most errors in BT/SST biases Mean Ch3b biases relative to N17: MetOp-A: -0.002 K NOAA-18: -0.014 K NOAA-19: -0.095 K NOAA-16: Unstable V1.00 V1.02 V1.10 Cross-platform inconsistencies are due to Sensor calibration systematic biases Spectral response function deviations from those used in CRTM Local time differences (affect SST and BTs through diurnal cycle) Work is underway to attribute the causes and reconcile different platforms 10 February 2010 Joint GRWG & GDWG Meeting Toulouse, France

Double-Differences in Ch4 and Ch5 V1.00 V1.02 V1.10 V1.00 V1.02 V1.10 Mean Ch4 biases relative to N17: MetOp-A: -0.039 K NOAA-18: -0.111 K NOAA-19: -0.151 K NOAA-16: Unstable Mean Ch5 biases relative to N17: MetOp-A: -0.036 K NOAA-18: +0.050 K NOAA-19: -0.061 K NOAA-16: Unstable 10 February 2010 Joint GRWG & GDWG Meeting Toulouse, France

Joint GRWG & GDWG Meeting Toulouse, France Conclusion Nighttime global BT biases in AVHRR IR bands on N17, -18, -19, and MetOp-A, show artificial variations up to several tenths of a Kelvin. NOAA-16 is out-of-family and unstable This variability likely arises from instabilities in Reynolds SST (used as input to CRTM). It largely cancels out when Double-Differences are calculated The DDs show that BTs are cross-platform consistent to within several hundredths of a degree Kelvin in all three IR bands Improved sensor calibration and response functions and accounting for diurnal variability is needed 10 February 2010 Joint GRWG & GDWG Meeting Toulouse, France

Ongoing and Future Work Work with NESDIS CAL experts (Changyong Cao, Fred Wu, Andy Harris, Jon Mittaz) to explore improving sensor radiances: calibration, response functions Work with CRTM Team (Yong Han) to improve daytime CRTM performance Work with Chelle Gentemann (RSS) to explore diurnal and skin-to-bulk corrections to Reynolds SST as input to CRTM in MICROS Check sensitivity of DDs to SST (Reynolds vs. RTG vs. OSTIA) upper air fields (GFS vs. ECMWF) ACSPO cloud mask 10 February 2010 Joint GRWG & GDWG Meeting Toulouse, France

Joint GRWG & GDWG Meeting Toulouse, France Back-Up slide M-O Biases in AVHRR Ch4 and Ch5 10 February 2010 Joint GRWG & GDWG Meeting Toulouse, France

Joint GRWG & GDWG Meeting Toulouse, France M-O biases in Ch4 and Ch5 M-O Biases in Ch4 M-O Biases in Ch5 V1.00 V1.02 V1.00 V1.10 V1.02 V1.10 Similar to Ch3B, warm M-O biases observed at all times for Ch4 and Ch5 The excursions of M-O biases in Ch4 and Ch5 are also observed However, they are smaller than in Ch3B due to more oblique atmosphere in Ch4 and Ch5 10 February 2010 Joint GRWG & GDWG Meeting Toulouse, France