The Lemur-2 satellites are 3-Unit CubeSats built and operated by NanoSatisfi, now named Spire Global, to establish a constellation of small, inexpensive satellites in operation for a number of purposes such as Earth observation, maritime monitoring, communications, meteorology and science. The first Lemur satellite launched in 2014 and carried a series of technical demonstration payloads plus two Earth observation systems operating in the visible and infrared wavelength ranges.
The Lemur-2 satellites carry two different payloads, SENSE, dedicated to maritime monitoring, and STRATOS for atmospheric measurements.
SENSE consists of an AIS receiver that can record signals sent by the Automatic Identification System of ships using the VHF frequency. The Automatic Identification System is used by sea vessels that send and receive VHF messages containing identification, position, course and speed information to allow the monitoring of vessel movements and collision avoidance as well as alerting in the event of sudden speed changes.
These signals can be transmitted from ship-to-ship and ship-to-shore to allow the monitoring of a local area, but deploying space-based AIS terminals allows a broad coverage and data relay to ground stations for monitoring of large sea areas. However, due to the large footprint of satellites, overlapping and signal collisions become a problem, especially for frequented traffic routes, requiring a steady improvement in reception technology to separate the different signals.
STRATOS makes use of GPS occultation measurements to determine temperature, pressure and humidity profiles of Earth’s atmosphere for application in operational meteorology.
The instrument consists of GPS receivers to be able to track the signals of several MEO satellites and measure the time delay and bend angle of signals that travel through the atmosphere located in the line of sight of the two spacecraft. These phase delay measurements due to refraction by the atmosphere can be made from the satellite altitude to very close to the surface leading to precise information on the properties of the atmosphere at an accurate vertical resolution.