Sentinel-1 Addon for DIAS
The Sentinel-1 mission is designed as a two-satellite constellation. The identical satellites orbit Earth 180Â° apart and at an altitude of almost 700 km. This configuration optimises coverage, offering a global revisit time of just six days.
At the equator, however, the repeat frequency is just three days and less than one day over the Arctic. Europe, Canada and main shipping routes are covered in less than three days.
Designed and built by a consortium of around 60 companies led by Thales Alenia Space and Airbus Defence and Space, the Sentinel satellites are an outstanding example of Europe’s technological excellence.
Each satellite, weighing 2300 kg, has been designed for a minimum lifetime of seven years in orbit. The design has benefited from experience gained with Canada’s Radarsat-2 and Italy’s Cosmo-SkyMed and uses the Piattaforma Italiana Multi Applicativa, PRIMA, satellite platform with a mission-specific instrument, the C-band synthetic aperture radar in this case.
As well as the 12-m long radar, the satellites each carry two 10 m-long solar wings. During launch, the solar wings and radar are folded up for protection and to fit into the Soyuz rocket fairing.
After the satellite is released into space, the solar wings and radar deploy together, but in a specific sequence that takes around 10 hours to complete. The sequence is unique, choreographed to ensure that both deploy in the safest possible way. The sequence also allows power from the wings to be available as soon as possible so that the satellite is independent.
The C-SAR instrument is designed and developed by EADS Astrium GmbH of Germany. The instrument provides an all-weather, day and night imaging capability to capture measurement data at high and medium resolutions for land, coastal zones and ice observations.
The C-SAR instrument is an active phased array antenna providing fast scanning in elevation (to cover the large range of incidence angle and to support ScanSAR operation) and in azimuth (to allow use of TOPS technique to meet the required image performance). To meet the polarisation requirements, it has dual channel transmit and receive modules and H/V-polarised pairs of slotted waveguides.
It has an internal calibration scheme, where transmit signals are routed into the receiver to allow monitoring of amplitude/phase to facilitate high radiometric stability.
SENTINEL-1’s metallised carbon-fibre-reinforced-plastic radiating waveguides ensure good radiometric stability even though these elements are not covered by the internal calibration scheme. The digital chirp generator and selectable receive filter bandwidths allow efficient use of on-board storage considering the ground range resolution dependence on incidence angle.
The key parameters of the SENTINEL-1 C-SAR instrument include:
Centre frequency: 5.405 GHz (corresponding to a wavelength of ~5.5465763cm cm);
Bandwidth: 0-100 MHz (programmable);
Polarisation: HH+HV, VV+VH, VV, HH;
Incidence angle: range 20°- 46°;
Look direction: right;
Antenna type: Slotted waveguide radiators;
Antenna size: 12.3 m x 0.821 m;
Antenna mass: 880 kg (representing 40% of the total launch mass);
Azimuth beam width: 0.23°;
Azimuth beam steering range: -0.9° to +0.9°;
Elevation beam width: 3.43°;
Elevation beam steering range: -13.0° to +12.3°;
RF Peak power: – 4.368 kW, – 4.075 kW (IW, dual polarisations);
Pulse width: 5-100 µs (programmable);
Transmit duty cycle: Max 12%, SM 8.5%, IW 9%, EW 5%, WV 0.8%;
Receiver noise figure at module input: 3 dB;
Maximum range bandwidth: 100 MHz;
PRF (Pulse Repetition Frequency): 1 000 – 3 000 Hz (programmable);
Data compression: FDBAQ (Flexible Dynamic Block Adaptive Quantization);
ADC sampling frequency: 300 MHz (real sampling);
Data quantisation: 10 bit;
Total instrument mass (including antenna): 945 kg;
Attitude steering: Zero-Doppler steering and roll steering.
DIAS supports the following list of product-types:
- Level-0: SM(1-6) ; EW ; IW
- Level-1: SM(1-6) SLC, GRD ; EW SLC, GRD ; IW SLC, GRD ; WV SLC, GRDM
- Level-2: SM(1-6) OCN ; EW OCN ; IW OCN ; WV OCN