The FORTE satellite was launched August 1997 into a 70 degree inclination orbit at 825 km altitude. Scientific instrumentation aboard the satellite includes both radio frequency (RF) and optical packages. The primary FORTE research payload includes two 20 MHz-bandwidth RF receivers, a 100 MHz-bandwidth RF receiver, an optical imager, and an optical photodiode detector. These instruments regularly record the radio and optical emissions from terrestrial lightning discharges. FORTE RF payloads and observations have been described by Massey et al.[1998b]; Jacobsonet al. [1999]; and Suszcynsky et al. [2000b]. The optical payloads, observations, and modeling have been described by Light et al. [2000]; Suszcynsky et al. [ 2000a, b].
A significant portion of the FORTE science effort has focused on the merging FORTE RF and optical observations with those from other satellite-based and ground-based resources. This data fusion has enhanced the value of FORTE observations in at least three respects: 1. Sensors with the ability to accurately geolocate sources have provided locations for events that FORTE has recorded but been unable to locate (FORTE's limited geolocation capabilities have been described by Suszcynsky et al. [2000a], Jacobson et al. [1999], and Jacobson and Shao [2000]; 2. Multiple characterizations of the same stroke, flash, or storm using different sensor types have provided insight into thunderstorm electrification and discharge processes that no single sensor has been able to provide; 3. Sensors capable of continuously observing storms have provided a context for FORTE data collection, which is limited to the observation of a single point on the ground for only fifteen minutes (at most) per 100-minute orbit. One surprising result of the current FORTE/NLDN comparison is a coincident event detection rate of only ~1% when FORTE is overhead the NLDN (personal comm., A. Jacobson). In order to understand the low FORTE/NLDN coincidence rates, further VLF/VHF comparisons are being undertaken using LASA as a system similar to NLDN, but providing complete waveform information as an improvement over the parameterization of waveforms provided by NLDN, and LDAR or LMA VHF systems.