# AMI Technical Details

A functional block diagram of the AMI hardware is shown in the figure. Its measurement functions are implemented by three modes of operation1: the image mode (SAR), the wave mode (SAR) and the wind mode (WNS). To achieve a low mass and to reduce cost and complexity several sub-systems (e.g. transmitters) are common to both the SAR and the Wind Scatterometer. As a result the SAR in image mode and the Wind Scatterometer cannot be operated in parallel, but the wind and wave modes are capable of interleaved operation - wind/wave mode.

In addition to the measurement modes, the AMI can be operated in experimental, calibration and support modes. The main experimental mode involves the tilting of the satellite around its roll axis by 9.5deg. to achieve a SAR incidence angle of approximately 35deg.. This roll tilt mode (RTM), performed during the first week of April 1992, has relevance to land application studies.

The operational capabilities of the AMI equipment, provided sufficien power is available on-board, are as follows:

- the SAR in image mode can be operated for a maximum of 12 minutes per orbit, either continuously or split to enable coverage of discrete segments - a maximum of six segments is planned (four on average) for each orbit
- in wave and wind measurement interleaved mode the AMI can be operated continuously
- it is not possible to operate the SAR for imaging and the Wind Scatterometer simultaneously.

The main technical characteristics of the AMI antennae are:
Frequency: 5.3 GHz (C-band)
Bandwidth: 15.55 +- 0.1 MHz
Peak power: 4.8 KW (at power amplifier out)
Polarisation: Linear Vertical
Antennae size: SAR - 10 m x 1 m
WNS - 2.5 m (mid) and 3.6 m (fore and aft)
Incidence angle: SAR - 23deg. nominal (35deg. in roll-tilt mode)
WNS -18deg.-47deg. (mid) and 25deg.-59deg. (fore and aft)
Transmit pulse width: 37.12 +- 0.06 micro-s (SAR); 70 micro-s and 130 micro-s (WNS)*
Quantisation: SAR image mode - 5I, 5Q (OGRC); 6I, 6Q (OBRC)
SAR wave mode - 4I, 4Q (OGRC); 2I, 2Q (OBRC)
WNS - complex I/Q 8 bits each
Signal-to-noise contribution: 308.3 dB Hz (SAR); 282.0 dB Hz (WNS)
Uncompensated gain stability: 4.6 dB (SAR) 4.1 dB and 4.8 dB (WNS)
Compensated gain stability: 1.84 dB (SAR); 0.3 dB and 0.48 dB (WNS)
Calibration pulse delay: 45 micro-s (SAR); 135 micro-s (WNS)
* where two figures are given for WNS the first one refers to the mid antenna and the second to the fore and aft antennae

## Active Microwave Instrument

  AMI Technical Details
  SAR Image Mode
  SAR Data Products

ESA Earth Observation