ERS-1 is the most sophisticated Earth observation satellite ever developed in Europe. It weighs well over two tons and, fully deployed, covers almost 12 metres. The satellite circles the Earth once every 100 minutes, 780 km up, beaming down data at a mind-boggling 105 megabits per second.
ERS-1's payload consists essentially of two specialised radars plus an infrared sensor. The Active Microwave Instrument - the biggest on-board system - produces extremely detailed images of a 100 km swath of the Earth's surface : 4.5 million pixels per second, downlinked directly to Earth. In wind and wave modes, the instrument measures continuously and globally wind speed and direction and ocean wave parameters.
The Radar Altimeter, the second instrument, measures with fantastic precision variations in the satellite's height above sea-level and ice. And the third Instrument, the Along-Track Scanning Radiometer, constructs detailed pictures of the thermal structure of the seas and oceans from surface temperature measurements correct to better than O.5 degrees Celsius.
In April 1995, ESA launched ERS-2, a carbon copy of ERS-1 with one important difference: ERS-2's payload includes a new instrument (GOME), purpose-designed to measure stratospheric and tropospheric ozone - an important step in the race to fully assess yet another environmental challenge. No other satellite can compete with ERS capabilities. On a global scale ERS is giving scientists more confidence in modelling the climate of our planet. Regionally it keeps a close eye on coastlines, marine pollution and land use changes.
SAR in Image Mode
The on-board SAR operated in image mode will obtain strips of high resolution imagery 100 km in width to one side of the satellite. The mid-swath depression, or incidence angle of the system in normal operation, will be 23 degrees . However, for some experimental applications the roll tilt capability of the satellite will be used to vary this up to 35 degrees .
The SAR image mode engineering parameters are as follows:
SAR antenna size: 10 m long, 1 m wide frequency: 5.3 GHz (C band) plus/minus 0.2 MHz bandwidth: 15.55 plus/minus 0.01 MHz PRF range: 1640-1720 Hz (in 2 Hz steps) long pulse duration: 37.1 plus/minus 0.05 microseconds compressed pulse length: 64 ns peak power: 4.8 kW polarisation: linear vertical signal sampling window: 299 Ás (99 km telemetered swath) A/D complex sampling: 18.96 Msamples/sec I and Q quantisation: 5 bits for OGRC, 6 bits for OBRC radiometric resolution: 2.5 dB at sigma-nought = -18 dB swath location: 244.5 km to the right of the orbital track swath width: 80.4 km (nominal within specifications) 102.5 km telemetered incidence angle: 23 degrees at mid-swath data rate: 105 Mbps
The following ERS SAR image mode products are available from CRISP: