An Intercalibrated Microwave Radiance Product for Use in Rainfall Estimation

Level 1C

Christian Kummerow, Wes Berg, G. Christian Kummerow, Wes Berg, G. ElsaesserElsaesser

Dept. of Atmospheric ScienceDept. of Atmospheric Science

Colorado State UniversityColorado State University

3rd IPWG WorkshopMelbourne, AustraliaOct. 23-27, 2006

Original Motivation

GPM will fly a constellation of radiometers to provide ~3-hourly sampling. If the radiometers are not inter-calibrated, neither will the rain rates.

Except for the dedicated GPM radiometers (GMI), the remaining set belongs to US and International agencies that have differing experience and requirements for calibration. These agencies may or may not support calibration activities once their own requirements are met.

Level 1C is an attempt to overcome political and programmatic issues and return “calibration” and data stewardship to the rainfall community

Level 1C aims to simplify formats and toolkits. “If a graduate student knows how to read data from one sensor, they can read it from all sensors”

TMI 10.7 19.4 21.3* 37 85.5 53.4º

AMSR-E 6.9 10.7 18.7 23.8 36.5 89 55.0º

SSM/I 19.4 22.2* 37 85.5 53.1º

SSMIS 19.4 22.2* 37 91.7 150** 183.3+/-1, 3, 7** 53.1º

WINDSAT 6.8 10.7*** 18.7*** 23.8 37*** 49.9º-55.3º

SensorIncAngChan Freq (GHz) *V-Pol only **H-Pol only ***V, H, +/45º, L, R

Today’s GPM constellation

AMSR-E Calibration Differences

Effect of SSM/I Calibration on rainfall

Inter-calibration Procedure

Select coincident overpasses (±30 min.) of TMI and SSM/I (other sensors will be done in same fashion but waiting for next version of algorithm below)

Use current retrieval method (OE in non-raining + PR adjustment in rain) to

derive geophysical parameter field that is consistent with each TMI Tb

Use geophysical parameters to compute Tb for each SSM/I sensor using appropriate channels, view angles and spatial resolution

Compute biases in computed SSM/I Tb versus observed Tb.

Use as much data as possible to reduce random errors.

SSM/I – TMI Crossover

TMI

SimulatedSimulated TBs vs Observed TBs

19 H (K) 21 V (K)

37 H (K) 85 V (K)

140120

140

160 180

160

180

120

265

245

225

205

205 225 245 265

135 155 175 195

195

175

155

135

300

280

260

240

240 260 280 300TMI

TMITMI

Simulated

Simulated

Simulated

SSM/I Calibration

SSM/I Calibration Offsets

Sat 19V 19H 22V 37V 37H 85V 85H

F11 -0.8 -2.1 -1.5 -0.3 -1.5 -1.4 -2.8

F13 -1.3 -2.1 -1.9 -1.2 -2.2 -0.8 -1.3

F14 -1.2 -1.7 -1.8 -1.8 -2.0 -0.9 -1.3

F15 -0.1 -1.9 -1.2 -0.9 -1.8 -0.1 -0.8

TMISSM/I F13SSM/I F14

AMSR-ESSM/I F15

19 H 19 V 22 V 37 H 37 V 86 H 86 V

+3

+2

+1

0

-1

-2

TB Bias (Simulated Minus Observed) in Kelvins

Approximate Channel Frequency

Level 1C Calibration Differences

Level 1C Projecthttp://mrain.atmos.colostate.edu/LEVEL1C

Pixel check for nonphysical values: Checks that individual antenna temperatures values are within physical limits (currently 50 to 325K), that lat/lon values are within range (-90 to 90 and -180 to 360), and that the distance between pixels along a scan are reasonable (10 to 30km).

Scan check for nonphysical seperation: Checks that the distance between adjacent scans (nadir point) is between 20 and 30 km. Scans outside of this range are flagged and are currently eliminated (not written out).

Scan check for deviations from climatology: Compares the antenna temperatures for each channel along the scan to climatological values. If more than 30% of the pixels along a given scan are greater outside the range of the mean climatological TA +/- 3 sigma, and this represents a change of 30% or more from the prior scan, the scan is flagged and eliminated (not written out).

Level 1C developmentQuality Control Procedures

Level 1C Data Availability

Naming Convention

F11.1C.CALT1.R1.19990303.37470.HDF

T : TMI was used as reference standard 1 : Maturity level

0: Nothing has been done to calibrate the Tb to the reference sensor1: Data has been re-calibrated to match the reference instrument2: The intercalibration has been verified by at least one independent effort3: The intercalibration has been accepted by the Precipitation Science Team

R : Revision number 1 : Initial Version

R2, R3 etc.) indicate substantive changes to the data, data format, and/or file contents, which imply reprocessing of the entire data record. Minor revisions to the files, such as might occur with a change to the metadata, are indicated by a lower case letter following the revision number (i.e. 1a, 1b, etc.).

Available Rainfall Maps