The French Systeme Probatoire d'Observation de la Terra (SPOT) Earth observing satellite system carries two High Resolution Visible (HRV) imaging sensors. First launched in 1986, the HRV provides high spatial resolution, with three spectral bands of visible and near-infrared data acquired at 20-m resolution, and a panchromatic band at 10-m resolution, as shown in the Figure of Observation Characteristics. The sensors can be pointed to either side of the orbital track, allowing the acquisition of stereo and repeat coverage in as short a period one or four days.
The high spatial resolution of the SPOT sensors has proven to be very useful for applications requiring highly detailed information. For situations where additional spectral information is desired at SPOT-equivalent resolution, the 10-m spatial resolution of the SPOT panchromatic data can be fused with Landsat Thematic Mapper (TM) data to bring the advantages of both types of data into the same image. Figure 1 illustrates the sharpening effect on Landsat TM image data achieved by merging the spatial component of the SPOT image data. Figure 2 is a satellite image of Baltimore, Maryland, produced with merged Landsat TM and SPOT panchromatic data.
HRV image data acquired by SPOT can be purchased from the SPOT Image Corporation through a network of distributors. The U.S. Geological Survey's Global Land Information System (GLIS) provides information on the sensor, and acquisition and availability of SPOT data.
The Figure of Observation Characteristics and SPOT Update in SPOT Image Corporation's newsletter SPOTlight (1993) provide information on improvements to SPOT 4, expected to be launched in 1997. In addition to a shortwave infrared band at 20-m resolution, the satellite will include a new independent sensor known as the Vegetation Monitoring Instrument (VMI). This sensor will acquire data with a wide-field scanning system, similar to that used by the Advanced Very High Resolution Radiometer, enabling global coverage on a daily basis with a ground resolution of 1 km at nadir (directly beneath the satellite).