The Defense Meteorological Satellite Program (DMSP) satellite is a polar orbiting satellite developed to support operations of the Department of Defense. The spacecraft is in a near-polar, sun-synchronous orbit at an altitude of approximately 835 km. The orbital period is 101.4 minutes, which produces 14.2 orbits per day. The operational system includes two satellites;observa-tions are made at near-local noon and midnight, and at dawn and dusk. The current satel- lites are F8, F9 and F10. F10 was launched in December 1990.
The primary image acquisition system on the DMSP satellites is the Operational Linescan System (OLS). The OLS scanner provides information in both the visible and the infrared. Additional sensors aboard all three of the current satellites are the Special Sensor Microwave Temperature (SSM/T), which are passive microwave temperature sounders. The F8 and F10 satellites also have Special Sensor Microwave Imaging (SSM/I) sensors, which are passive microwave radiometers.
As a rule, data from the DMSP are transmitted in encrypted form. The decrypters, known as KG-44s, are in short supply. However, more could be built if there is sufficient demand for them. Permission to have a KG-44 and KEY material, a COMSEC (computer security equipment) account must be acquired from the National Security Agency. The KG-44 and KEY material are both classified SECRET CRYPTO and must be protected accordingly.
By special arrangement between the National Science Foundation and the Department of Defense, the DMSP transmits only unencrypted data when over Antarctica. This arrangement was due to an international treaty on the demilitarization of the Antarctic. There is no effort at this time to transmit unencrypted data anywhere else in the world. SeaSpace, one of the vendors discussed later in this report, has developed a system which receives and processes this clear text DMSP data.
DMSP data are normally transmitted at 1-megabyte per second with high-resolution OLS coverage of 0.3 nm. Starting with the F-10 DMSP, data are also transmitted at a 66 kilobit/sec rate (this rate is known as Realtime Data Smooth (RDS) with a 1.5-nm resolution for the OLS data. All sensors aboard will be transmitted in this mode. The Air Force is recommending that the KEY material used in the encrypter (KG-46) be downgraded from Secret to Unclassified. This would reduce the handling problems on the ground equipment if approved. A Small Tactical Terminal (STT) to receive and decode such data is currently under development by the Space Systems Division (SSD) of the Air Force. About 300 of the terminals will be placed in the field. The STTs are expected to come on-line in 1994.
Should ARM decide that real-time access to DMSP data is necessary, the ARM Program Office can contact the Program Director of the DMSP to discuss the possibility of receiving the encrypted data.
The National Snow and Ice Data Center (NSIDC) plans to archive digital DMSP/OLS data. The data will be available two to three weeks after being collected. The data to be archived will include global coverage with a resolution of 2.7 km, with high resolution coverage at 0.3 nm available for limited areas. The new system is tentatively scheduled for implementation in mid-1991. NSIDC also maintains the archive of digital SSM/I data. The SSM/I data are available two to three months after being collected. The Center is trying to improve turnaround time; however, it cannot guarantee anything better than the time stated. The Center is not funded to process SSM/T data and does not do so.