Remote sensing

Remote sensing is the collection of data about the Earth's surface, oceans or atmosphere from a distance, using sensors mounted on satellites, aircraft or drones rather than instruments placed on site. Sensors can be passive, recording reflected sunlight or emitted heat, or active, like radar and lidar, which send a signal and measure its return.

Raw sensor output is a grid of measurements across wavelength bands; deriving something useful, such as land cover, vegetation health or sea-surface temperature, requires calibration, atmospheric correction and an index or classification model. The normalized difference vegetation index is a widely used example, built from just two of those bands. This differs from satellite imagery analysis, which specifically covers workflows applied to satellite-sourced imagery, whereas remote sensing is the broader category that also includes airborne and drone sensors.

Remote sensing feeds environmental monitoring, agriculture, disaster response and defense applications, and is typically loaded into a geographic information system for further spatial analysis alongside other location data. The main pitfalls are cloud cover and atmospheric interference that corrupt optical imagery, and mistaking a sensor's spatial resolution for its accuracy, a fine-resolution image can still carry large measurement error.