The Goddard Profiling Algorithm (GPROF) is a physically based retrieval of hydrometeor (vertical) profiles that best fit the available channels of passive radiometer data. In this case it is applied to the 7 channels of microwave data from the Special Sensor Microwave/Imager (SSM/I) that are carried on selected Defense Meteorological Satellite Program (DMSP) satellites that fly in sun-synchronous low-earth orbits. Each hydrometeor profile is associated with a surface precipitation rate. GPROF retrieves all parameters using the estimated expected value (a Bayesian method) described in Kummerow et al. (1996). Over ocean, convective/stratiform classification is performed, and convective rain rates are assigned in concentric rings, as described in Olson et al. (1999).
The GPROF 6.0 Gridded Orbits data set is computed with GPROF Version 6.0 for all useful data from all SSM/I sensors. This provides a single satellite (with gaps) from July 1987--December 1991 and at least 2 satellites since then. There are a total of 9 gridded fields providing surface rainrate, number of samples, and information on time, quality, and vertically integrated liquid and ice content.
The data set archive consists of unformatted sequential writes of INTEGER*2 and INTEGER*1 fields. For the period July 1987--December 1999 each file consists of a full orbit that begins with the ascending equatorial crossing. Due to a change in the source of SSM/I data, thereafter each file consists of a half-orbit starting at the north or south turning point of the orbit. The volume per file is about 3.3 MB (or 40 KB compressed, since each file is mostly empty space). The grid on which each field is presented is a 0.5°x0.5° latitude--longitude (Cylindrical Equal Distance) global array of points. It is size 360x720, with X (latitude) incrementing most rapidly north to south, and then Y (longitude) incrementing east to west starting at the Prime Meridian. Whole- and half-degree values are at grid edges:
First point center = (89.75°N,0.25°E)
Second point center = (89.25°N,0.25°E)
Last point center = (89.75°S,0.25°W)
Missing values are denoted by the value -9999., and the units on the fields depend on the variable. For example, rainfall is carried as 0.01mm/hr.
The standard references are:
Kummerow, C., W.S. Olson, and L. Giglio, 1996: A simplified scheme for obtaining precipitation and vertical hydrometeor profiles from passive microwave sensors. IEEE Trans. Geosci. Remote Sens., 34, 1213-1232.
Olson, W.S., C.D. Kummerow, Y. Hong, and W.-K. Tao, 1999: Atmospheric latent heating distributions in the tropics derived from satellite passive microwave radiometer measurements. J. Appl. Meteor., 38, 633-664.
The dataset creator is:
Eric J. Nelkin
Code 613.1
NASA Goddard Space Flight Center
Greenbelt, MD 20771 USA
Phone: +1 301-614-6311
Fax: +1 301-614-5492
Internet: eric.j.nelkin@nasa.gov