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Unmanned Earth Resources Satellites


Unmanned Earth resources satellites are satellites equipped with remote sensing instruments used to collect images and environmental data from the Earth's surface without a crew onboard.
They help monitor:

  • land use

  • vegetation

  • soil and water resources

  • climate

  • oceans

  • atmosphere

  • natural hazards

These satellites are grouped based on the type of radiation they measure and the sensors they carry.

Five Groups of Unmanned Earth Resources Satellites

Remote sensing satellites can be categorized into five main groups, based on the wavelengths they record and the type of environmental information they collect.

First-Generation Earth Resources Satellites

Wavelength region: Visible and Near-Visible (VNIR)

✔ Characteristics

  • Use multispectral scanners

  • Record reflected sunlight

  • Mainly for land use, vegetation, and surface mapping

✔ Example

  • Landsat series (Landsat 1, 2, 3)
    These were the first generation of Earth resource satellites launched in the 1970s.

Second-Generation Earth Resources Satellites

Wavelength region: Visible and Near-Visible (VNIR)

✔ Characteristics

  • Improved spatial resolution

  • More spectral bands

  • Higher radiometric sensitivity

✔ Examples

  • SPOT (Satellite Pour l'Observation de la Terre)

  • Later Landsat missions (Landsat 4, 5, 7)

SPOT introduced high-resolution panchromatic imagery and along-track stereo capability, which greatly advanced remote sensing.

Thermal Infrared Satellites

Wavelength region: Thermal Infrared (TIR)

✔ Characteristics

  • Measure emitted heat energy

  • Useful for temperature mapping

  • Work both day and night

✔ Examples

  • HCMM (Heat Capacity Mapping Mission)
    A NASA mission designed to study thermal behavior of land surfaces.

Microwave Remote Sensing Satellites

Wavelength region: Microwave (active or passive)

✔ Characteristics

  • Can penetrate clouds, smoke, and light rain

  • Work day and night

  • Include both active radar and passive microwave sensors

✔ Examples

  • Seasat (first ocean-related radar satellite)

  • ERS-1 (European Remote Sensing Satellite)

  • RADARSAT (Canadian radar satellite)

These satellites are extremely useful for:

  • flood mapping

  • soil moisture

  • sea-ice monitoring

  • land deformation (InSAR)

Polar Platform Satellites

Orbit: Polar orbit / Sun-synchronous orbit

✔ Characteristics

  • Carry a wide range of multispectral, thermal, microwave, and atmospheric sensors

  • Provide continuous, long-term environmental monitoring

  • Serve as major data sources for climate and environmental studies

✔ Examples

  • NOAA Polar Orbiters

  • EOS (Earth Observing System) satellites such as:

    • Terra

    • Aqua

    • Aura

These satellites will continue to provide vital environmental data well into the future.


GroupWavelengthsPurposeExamples
1Visible + NIRFirst-generation multispectral satellitesLandsat 1–3
2Visible + NIRSecond-generation multispectral satellitesSPOT, Landsat 4–7
3Thermal IRHeat and temperature mappingHCMM
4MicrowaveRadar and microwave sensingSeasat, ERS-1, Radarsat
5Polar PlatformsMultisensor environmental observationTerra, Aqua, Aura, NOAA


Unmanned Earth resources satellites are remote sensing platforms carrying different sensors to monitor Earth's surface. They are grouped into five types based on the wavelengths they detect: visible/NIR (Landsat, SPOT), thermal (HCMM), microwave (Seasat, ERS-1, RADARSAT), and multisensor polar platforms (Terra, Aqua, NOAA). These satellites provide critical environmental data for physical geography and Earth science.


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