# Operational Capabilities

The ERS-1 mission is global, however, its pre-operational nature and some technical and practical considerations, e.g. satellite power-supply capability and ground station coverage, impose limits to the achievable payload duty cycle and, therefore, flexibility is a major requirement in establishing payload operating modes.

The satellite availability is defined as the proportion of time for which valid measurements are made by the satellite and corresponding data is transmitted. Causes of non-availability will include link disturbances, e.g. rain, and opera-tional constraints, such as shadowing, planned re-configuration, manoeuvres for altitude correction and repeat cycle changes. With the exclusion of satellite and instrument failures and the execution of experimental modes, e.g. roll-tilting, satellite availability will be not less than 95% from the end of the commissioning phase until three years after launch.

The low bit rate (LBR) instruments - Radar Altimeter, Wind Scatterometer, SAR in wave mode and the ATSR, will be operated to provide as much global coverage, with an observation priority of oceans, then permanent ice sheets and finally land areas. Over the ocean the Radar Altimeter and Wind Scattero-meter will operate continuously with an interleaved SAR wave mode every 200 km. The ATSR will operate continuously for long periods (at least several days, nominally on a permanent basis) over ocean, ice and land surfaces. Data acquisition for the LBR instruments may be limited by energy shortages, on-board recoring capacity and conflicts between wind/wave mode and the SAR image mode in coastal areas. The figure shows the comparative positioning of the swath coverage for different instrument measurement modes.

The SAR mission is built around the user requests and a plan to obtain a set of regional coverages of specific land/ice surfaces and coastal areas of interest. The aims for image acquisition are as follows:

- annual collection of full data sets of land surfaces, coastal areas and permanent ice sheets for each ground station coverage area
- regular revisits of selected areas for monitoring renewable resources, coastal areas and the marginal sea/ice zones.

It is assumed that the SAR can be operated for 12 minutes per orbit (up to two minutes during eclipse), either without interruption or split to enable coverage of discrete (up to a mximum of six per orbit, and not exceeding an average of four over the lifetime of the satellite). Each segment will have a minimum length of at least one minute, and consecutive segments will be separated by at least 30 seconds.

## ERS-1 Overview

  Satellite Concept
  ERS-1 Orbit
  Payload Summary
  Operational Capabilities
  ERS-1 Specification Table

ESA Earth Observation