The multiple scales covered by SKIM are related to the time sequence of operation of the radar, also known as "chronogram". With a carrier frequency around 35.75 GHz, the signal within a pulse is modulated to chirp with a 200 MHz bandwidth. The processing can use this fast variation in frequency to perform a range compression (leading to the 0.75 m line of sight resolution, which projects to 3.75 m on the ground at 12° incidence).
- pulse duration : a few microseconds
- cycle of pulses sent with the same beam : 30 milliseconds
- macro-cycle with all beams: 0.24 s
- mega-cycle with a full azimuth turn of all the beams : ~ 10 s
- half-orbit around the globe: ~ 30 minutes
- period of orbits (passing back at exactly the same point along the track) : to be decided, possibly 11, 25 or 27 days.
- mission duration : 5 years
SKIM is designed to be "on" all the time, acquiring data on land, ice & oceans.
1. Time Sequence
The SKIM radar works with only one beam active at any given time. As a result, the pulses ( around 32000 of them per second) are transmitted an received by the same feed horn corresponding to the same beam.
2. Spatial patterns and Coverage
- globe: The largest time scale, the orbital period (11, 27 or 29 days depending on the orbit choice) defines the revisit time and the sequence of measurement at any given location. The full globe is covered, except for latitudes higher than 82.5°.
- single swath: the swath is around 300 km wide (depending on the exact orbit altitude)
- footprint: each footprint is 6 km in diameter
- azimuth resolutuon: around 300 m
- range resolution : 3.75 m at 12° incidence (outer beams).
Other spatial scales of interest:
- radar wavelength : 8 mm, which projects to 4 cm on the ground
- delta-K wavelengths: 12, 20, and 60 m