Level 1C Overview   «   Home

Calibration standard Date sources Software Version numbers Beyond the prototype

                The GPM framework requires that radiometers flying on different satellites be intercalibrated in order to insure a consistent framework for the rainfall algorithms. These intercalibrated radiances, termed Level 1C products within GPM, are not an attempt to replace the Level 1B calibrated radiances for which instrument owners have basic responsibility. Instead, Level 1C attempts to homogenize the existing L1B products to insure that differences in the rainfall products among sensors are not due to differences in the official calibration provided for each sensor.

  Calibration standard:

We currently use TMI level 1B data as the standard for intercalibration. By this, we do not imply that TMI is better calibrated than any other sensor. We chose TMI merely because it is the precursor to the GPM Microwave Imager that becomes a natural calibration reference in the GPM era.

  Date sources:

To insure the traceability of Level 1C products, all procedures leading to the Level 1C product use the 'official' archived data and calibration procedures written by the responsible agency as input. This insures that everyone has access and can reproduce/improve upon the stated procedures.

  Software:

Version 2005 represents our first attempt to intercalibrate SSM/I to TMI sensors in an open and documented fashion. In doing so, we have paid nearly as much attention to the framework that will be required for future improvements as we have to the intercalibration itself. As such, we have attempted to outline exactly what we did with enough information for others to reproduce. While the documentation is critical, we are not making the intermediate data or software available. This could become an intractable problem for us, or anyone else wishing to improve upon the current procedure.

  Version numbers:

The intercalibration procedures should use the year (e.g. 2005) as a version number in order to isolate the procedures themselves from any version numbering scheme used by the operational data processing systems. The documentation should clearly state the source and version numbers of any input data.

  Beyond the prototype:

We expect this information to reside permanently at the Precipitation Processing System which has primary responsibility for GPM rainfall processing. As intercalibration practices improve and mature, we expect information similar to that provided for each sensor to be provided whenever an new Level 1C is used by the PPS.