Satellites

Adapted from the article on https://appliedsciences.nasa.gov/join-mission/training/english/arset-fundamentals-remote-sensing

Satellites carry sensors or instruments. The names of sensors are usually acronyms that can include the name of the satellite.

Satellite Characteristics

  • Orbits: Low-Earth Orbit vs. Geostationary
  • Energy Source: Passive vs. Active
  • Solar and Terrestrial Spectra: Visible, UV, IR, Microwave…
  • Measurement Technique: Scanning; Non-Scanning; Imager; Sounders
  • Resolution Type and Quality: Spatial, Temporal, Spectral, Radiometric
  • Application: Weather, Ocean Color, Land Mapping, Air Quality, Radiation Budget, etc.

Types of Satellite Orbits

Geostationary–

  • Satellites are typically ~36,000 km over the equator with the same rotation period as Earth
  • Multiple observations per day 
  • Limited spatial coverage – observations are always of the same area
  • Examples: Weather or communications satellites

Low Earth Orbit–

  • Circular orbit moving relative to Earth at 160-2,000 km – can be polar or non-polar
  • Less frequent measurements
  • Large (global) spatial coverage
  • Examples (polar): Landsat or Terra

Polar Orbiting

Provides global coverage and measurement frequency can vary from 1 measurement per day to 1 per month.

Non-Polar Orbiting

Does not provide global coverage. The measurement frequency can vary every few hours to a few weeks.

Passive vs. Active Sensors

There are two types of ways remote sensing data is collected: passive and active remote sensing.

Passive remote sensing: depends on changes in gravity or reflected and emitted radiation from the Earth. For instance, the Grace Follow-On satellites measure changes in the Earth’s gravity. Landsat, the MODIS sensor onboard Terra & Aqua, and Aqua’s AIRS sensor, all depend on changes in the reflected and emitted radiation from the Earth for data.
Examples: Landsat, MODIS (Terra/Aqua), AIRS (Aqua), GRACE

Active remote sensing: an instrument sends beams of radiation and measures its return.
Examples: Radar, LIDAR

Passive sensors detect only what is emitted from the landscape, or reflected from another sources (e.g., light reflected from the sun).

Active instruments emit their own signal and the sensor measures what is reflected back. Sonar and radar are examples of active sensors.

Posted on July 13, 2021 Tags: