# THE FUTURE

# SPOT 5

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## Mission and system description

### Continuity of service and new features

Following SPOT 4, the SPOT family will provide service continuity with SPOT 5 for which CNES is designing a new imaging instrument High Resolution Geometry or HRG. SPOT 5 will offer new capabilities and performance to answer the growing demand in cartography, agriculture, planning and environment.

Ariane will place SPOT 5 in the same orbit as SPOT 1, 2, 3 and 4, i.e. a circular, quasi-polar orbit at an altitude of 830 km and a pass over the equator at 10.30 a.m. (local time at descending node).

The main payload consists of high resolution imaging instruments delivering the following product improvements compared to SPOT 4:

- higher ground resolution: 5 meters and 3 meters (instead of 10 m) in panchromatic mode,
- higher resolution in multispectral mode: 10 m (instead of 20 m) in all 3 spectral bands in the visible and near infrared ranges. The spectral band in the intermediate infrared (essential for Vegetation data) is maintained at a resolution of 20 m due to limitations imposed by the geometry of the CCD sensors used in this band,
- field width of each instrument: 60 km,
- the oblique viewing capacity of each instrument is maintained, providing rapid access to a given area,
- possibility of a dedicated instrument for along track stereo acquisition on board SPOT 5: decision in 1998.

Spectacular breakthroughs in a wide range of technologies have made these performance improvements possible:

- 12,000-point linear sensor arrays,
- very high dimensional stability materials,
- data compression systems,
- high capacity static memory.

As was the cas for previous satellites, SPOT 5 is being developed in cooperation with Sweden and Belgium.

### Spectral band continuity and improved spatial resolution

The SPOT 5 spectral bands will be the same as those for SPOT 4: B1 (0.50-0.59 µm); B2 (0.61-0.68 µm); B3 (0.79-0.89 µm); and MIR (1.58-1.75 µm). The panchromatic band will, however, return to the values used for SPOT -1/ -3 (Pan: 0.51-0.73 µm). As requested by many users, this will ensure continuity of the spectral bands established since SPOT 1 (see Louahala 1993). Spatial resolutions will, on the other hand, be improved within the limits of technical feasibility as the field width of each instrument will be also kept identical. The high-resolution panchromatic mode will go from 10 m to 5 m and 3 m and the multispectral mode (B1, B2, B3) from 20 to 10 m.

These choices reconcile the desire to transmit the largest possible volume of useful data while remaining within a data rate limit of 150 Mbit/s using data compression techniques compatible with multi-resolution imagery.

The decision as to which channel should offer 5 m and 3 m resolution was based on the results of a large number of experiments with both SPOT data and simulated high-resolution data. There was a clear preference (55%) for high-resolution panchromatic data, particularly for the visual interpretation of fine detail (cf. Sempere, 1994). The second preference was the near infrared (45%) which would have been useful for areas affected by haze.

### Radiometric and geometric quality

Customers using SPOT data for mapping applications are the most demanding as regards image geometry. They should be happy with SPOT 5 data. The specifications call for a planimetric accuracy of 10 m (rms) and an elevation accuracy of 5 m (rms). These figures are compatible with conventional mapping standards at 1:50 000 scale.
Whether measured in terms of the MTF or noise, the radiometric quality of SPOT 5 imagery will be equal to or better than that of SPOT 4. Thematic interpretation specialists are assured of good visual interpretation and good control during digital processing.