The U.S. Air Force program in meteorology, essential to its military operations, began with the launch of the first DMSP (Defense Meteorological Satellite Program) satellite on September 16, 1966. The principal instrument is the OLS (Operational Linescan System) which images in both the visible and thermal IR. This program, involving many launches in several series, continues today and much of its data are declassified. Below is a TIR image of Hurricane Henrietta, spawned in the East Pacific, which struck the west coast of Mexico on September 5, 1955.

Later DMSPs also carry the Special Sensor Microwave Imager (SSM/I) which measures vertically and horizontally polarized radiation at 19.36, 22.23, and 85.5 GHz and horizonatally at 37.0 GHz. Here is a global brightness temperature map derived from Channel 2 data for July 9, 1996:

This sensor, kin to SMMR, seeks to detect rainfall and clouds, such as displayed in this world map showing Total Precipitable Water (in g/cc), determined from SSM/I data, for September 3, 1987:

Over the course of a full year, SSM/I readings can be averaged out to provide a global map that summarizes annual rainfall (in millimeters), as presented in this example:

The first satellite whose primary mission is to measure precipitation is TRMM (Tropical Rainfall Mapping Mission), a joint research project between the U.S. (NASA) and Japan (NASDA: National Space Development Agency). A basic objective of TRMM is to obtain estimates of the vertical profile of the latent heat (heat resulting from a change of state) released through condensation of water vapor in the atmosphere, especially in the Equatorial Intertropical Convergence Zone (ITCZ). The TRMM is a large spacecraft that was built at NASA's Goddard Space Flight Center and successfully launched in Japan on November 27, 1997. The TRMM Observatory has three primary instruments:

1. The Precipitation Radar (PR), built in Japan, capable of making 3-D rainfall distribution measurements. The PR is an electronically scanning radar that operates at 13.8 GHz using horizontal polarization with a 129-slotted waveguide antenna. It has a horizontal resolution of 4.3 km at nadir and a scanning swath width of 220 km.
2. The Multi-Channel Microwave Radiometer (TMI), which seeks information on the integrated column precipitation content, its areal distribution, and its intensity. The TMI operates at 5 frequencies, ranging from 10.65 GHz (45 km spatial resolution) to 85.5 GHz (5 km resolution); dual polarization at 4 of the frequencies provides 9 channels; at 65Á scan angle the swath width is 760 km.
3. The Visible Infrared Scanner (VIRS) to provide high resolution (2.1 km at nadir) information on cloud cover, cloud type, and cloud top temperatures, being a radiometer operating at 0.63, 1.6, 3.75, 10.8, and 12.0 mm.

In addition, the spacecraft's load includes the Lightning Imaging Sensor (LIS) (at 0.777 mm) capable of picking out lightning flashes associated with active rainfall and the Clouds and Earth's Radiant Energy System (CERES), a broad band scanning radiometer designed to measure reflected and emitted radiative energy at the surface and for the atmosphere and its constituents.

A goal of this low-altitude (350 km), non-sun-synchronous (precessing) satellite is provide monthly precipitation data over 500 x 500 km grids, especially for the tropical oceans regions. A network of ground stations to produce corroborating ground truth is under development. More information and updates on this spacecraft and its products can be found at this NASA Goddard Home Page: http://trmm.gsfc.nasa.gov

By December, 1997 the first images from TRMM had been released to the Net. We reproduce three representative ones here; others can be accessed via the above URL.

The first compares images over the Hawaiian Islands obtained simultaneously by TRMM's TMI sensor (left) and the SSM/I on the current DMSP satellite. The improved resolution of the TMI is evident. The islands were largely cloud-covered with localized rainfall (reds).

The second image show Typhoon Pam in the western Pacific south of Okinawa in early December. The imaged cloud tops appear gray; the colors in the flat projection represent relative rainfall intensities; the side view (cross-section) is an extrapolation of data to indicate rain distribution within the cloud mass.

The next image is a composite from several days coverage showing worldwide rainfall during part of December. Major cloud masses are in white; areas of moderate or intermittent rainfall in purple; and heavier rains in reds, yellows, and greens. Can you locate a small hurricane in this image?

---

[an error occurred while processing this directive] [an error occurred while processing this directive]