Which data type is NOT typically provided by Earth-observing satellites for environmental monitoring?

• A. Surface temperature.
• B. Vegetation indices.
• C. Seafloor bathymetry.
• D. Land-cover data.

Answer: (C)

Satellites are excellent for observing conditions at or near the surface, using different sensors to measure temperature, vegetation, and land cover. Surface temperature is derived from thermal infrared or microwave sensors that detect heat emitted by the land or water surface. Vegetation indices come from analyzing the red and near-infrared reflectance of plants, which indicates green vegetation health and cover. Land-cover data results from classifying multispectral imagery into categories like forest, urban, or cropland, providing a map of how the land is used.

Mapping the seafloor, however, requires depth information that light and radio waves cannot reliably provide once they travel through water. The sea attenuates and scatters these signals, so direct measurements of depth come from sonar or depth-sounding systems mounted on ships or submarines. Satellite altimetry can give related information about sea-surface height and indirect clues about underwater features, but it does not deliver direct bathymetric measurements. For environmental monitoring, the seafloor bathymetry data are not typically provided by Earth-observing satellites, making it the outlier among the listed data types.