Satellite Systems
A comprehensive survey of Earth observation satellite platforms, from open-access missions to commercial constellations
Copernicus Sentinel Constellation
The European Space Agency's Copernicus programme operates the Sentinel family of satellites, providing free and open data for environmental monitoring. Each mission targets a specific observation domain.
Sentinel-1 (SAR)
Instrument
C-band SAR (5.405 GHz)
Revisit Time
6 days (constellation) / 12 days (single)
Resolution (IW mode)
5 x 20 m (range x azimuth)
Swath Width
250 km (IW mode)
Polarization
VV, VH (dual-pol) or HH, HV
Key Applications
InSAR, flood mapping, sea ice, ship detection
Sentinel-1A launched April 2014, Sentinel-1B December 2021 (failed August 2022). Sentinel-1C launched December 2024 to restore the constellation. All-weather, day-and-night imaging capability makes SAR essential for operational monitoring.
Sentinel-2 (MSI)
Instrument
Multi-Spectral Instrument (MSI), 13 bands
Revisit Time
5 days (constellation) / 10 days (single)
Resolution
10 m (VNIR), 20 m (red edge/SWIR), 60 m (atm.)
Swath Width
290 km
Spectral Range
443 nm - 2190 nm (VNIR + SWIR)
Key Applications
NDVI, LULC, agriculture, water quality
Sentinel-2 is the workhorse of optical EO. Its 13 spectral bands include 4 red-edge bands (B5-B7, B8a) specifically designed for vegetation monitoring. Level-2A products include bottom-of-atmosphere (BOA) reflectance with the Sen2Cor processor.
Sentinel-3 (OLCI / SLSTR / SRAL)
Instruments
OLCI (21 bands), SLSTR (9+2 bands), SRAL
Revisit Time
<2 days (constellation)
Resolution
300 m (OLCI), 500 m-1 km (SLSTR)
Swath Width
1270 km (OLCI), 1420 km (SLSTR)
Orbit
Sun-synchronous, 814 km altitude
Key Applications
SST, ocean color, fire detection, altimetry
Sentinel-3 provides global, medium-resolution coverage optimized for ocean and land surface monitoring. SLSTR fire channels operate at 1 km resolution in both day and night. SRAL radar altimeter measures sea surface height.
Sentinel-5P (TROPOMI)
Instrument
TROPOMI (UV-VIS-NIR-SWIR spectrometer)
Revisit Time
~1 day (near-global daily coverage)
Resolution
5.5 x 3.5 km (upgraded from 7 x 3.5 km)
Swath Width
2600 km
Species Measured
NO2, O3, SO2, CO, CH4, HCHO, aerosols
Key Applications
Air quality, GHG monitoring, ozone layer
Sentinel-5P is the first Copernicus mission dedicated to atmospheric composition monitoring. TROPOMI measures trace gases with unprecedented spatial resolution, enabling city-level air quality assessment and methane leak detection.
Landsat 8 & 9 (USGS/NASA)
The Landsat program provides the longest continuous space-based record of Earth's land surface, spanning over 50 years since Landsat 1 (1972). Landsat 8 and 9 form the current operational pair.
Landsat 8 (2013)
- OLI: 9 bands, 30 m (15 m pan), 185 km swath
- TIRS: 2 thermal bands at 100 m (resampled 30 m)
- Revisit: 16 days (8 days with Landsat 9)
- Orbit: Sun-synchronous, 705 km, 10:00 AM LTAN
- Quantization: 12-bit (improved from 8-bit)
Landsat 9 (2021)
- OLI-2: Same 9 bands as OLI, improved SNR
- TIRS-2: Fixed stray light issue from TIRS-1
- Quantization: 14-bit (2x radiometric improvement)
- Calibration: Improved absolute accuracy
- Data: Free and open via USGS EarthExplorer
Landsat Next (est. ~2030): The next generation will feature 26 spectral bands (up from 11), 10 m spatial resolution, and a constellation of 3 satellites providing 6-day revisit. This represents a major leap in capability for the Landsat continuity mission.
MODIS & VIIRS
Moderate-resolution imagers designed for daily global monitoring of land, ocean, and atmospheric processes.
MODIS (Terra & Aqua)
- Bands: 36 spectral bands (0.4 - 14.4 um)
- Resolution: 250 m (2), 500 m (5), 1000 m (29)
- Swath: 2330 km (near-daily global)
- Terra: 10:30 AM descending (1999-present)
- Aqua: 1:30 PM ascending (2002-present)
- Products: MOD09 (surface reflectance), MOD11 (LST), MOD13 (NDVI), MOD14 (fire)
VIIRS (Suomi NPP & JPSS)
- Bands: 22 bands (0.4 - 12.5 um) + DNB
- Resolution: 375 m (I-bands), 750 m (M-bands)
- Swath: 3040 km
- DNB: Day/Night Band (nighttime lights)
- Status: Heritage successor to MODIS
- Products: VNP09 (reflectance), VNP14 (fire), VNP46 (nighttime lights)
Geostationary: GOES & Meteosat
Geostationary satellites orbit at ~35,786 km altitude, matching Earth's rotation to provide continuous monitoring of the same hemisphere. Critical for weather nowcasting, severe storm tracking, and fire detection.
GOES-16/17/18 (NOAA)
- ABI: 16 bands, 0.5-2 km resolution
- Cadence: Full disk every 10 min, CONUS 5 min, mesoscale 1 min
- GLM: Geostationary Lightning Mapper
- Coverage: Western Hemisphere
- GOES-18: Operational West (2022-present)
Meteosat Third Gen (EUMETSAT)
- FCI: 16 channels, 0.5-2 km resolution
- Cadence: Full disk every 10 min
- IRS: InfraRed Sounder (first on GEO)
- Coverage: Europe, Africa, Indian Ocean
- MTG-I1: Launched December 2022
Altimetry & Gravity Missions
ICESat-2 (NASA, 2018)
- Instrument: ATLAS (photon-counting lidar)
- Wavelength: 532 nm (green laser)
- Along-track: 0.7 m shot spacing
- Accuracy: ~2 cm elevation (flat ice)
- Applications: Ice sheet mass balance, sea ice freeboard, vegetation canopy height, bathymetry
GRACE-FO (NASA/DLR, 2018)
- Concept: Twin satellites, 220 km apart
- Measurement: Inter-satellite range change (microwave + laser)
- Sensitivity: ~1 cm equivalent water thickness
- Resolution: ~300 km spatial, monthly temporal
- Applications: Groundwater depletion, ice mass loss, sea level budget
Commercial Constellations
Commercial providers offer very high resolution (VHR) and high-cadence imagery, filling gaps that open-access missions cannot address.
Planet Labs
- PlanetScope: ~200 Dove CubeSats, 3-5 m, daily global
- SkySat: 21 satellites, 0.5 m resolution
- SuperDove: 8 spectral bands
- NICFI: Free tropical forest basemaps (Norway-funded)
Maxar (DigitalGlobe)
- WorldView-3: 31 cm pan, 1.24 m MS, 8 SWIR bands
- WorldView Legion: 6 satellites, 30 cm, 15x daily revisit
- Products: Stereo DEM, 3D surface models
- Access: Commercial license, GBDX platform
Mission Comparison
| Mission | Type | Resolution | Revisit | Bands | Access |
|---|---|---|---|---|---|
| Sentinel-1 | C-band SAR | 5 x 20 m | 6 days | VV/VH | Free |
| Sentinel-2 | Optical MSI | 10-60 m | 5 days | 13 | Free |
| Sentinel-3 | OLCI/SLSTR | 300 m - 1 km | <2 days | 21+11 | Free |
| Sentinel-5P | Spectrometer | 5.5 x 3.5 km | ~1 day | UV-SWIR | Free |
| Landsat 8/9 | OLI/TIRS | 15-100 m | 8 days | 11 | Free |
| MODIS | Imaging rad. | 250 m - 1 km | 1-2 days | 36 | Free |
| GOES-18 | GEO imager | 0.5-2 km | 1-10 min | 16 | Free |
| ICESat-2 | Lidar | ~14 m footprint | 91 days | 532 nm | Free |
| PlanetScope | Optical | 3-5 m | Daily | 4-8 | Commercial |
| WorldView-3 | Optical VHR | 0.31 m | <1 day | 29 | Commercial |
Key Takeaways
There is a fundamental trade-off between spatial resolution and revisit time/swath width.
SAR (Sentinel-1) is the only option for all-weather, day-and-night monitoring.
Sentinel-2 + Landsat 8/9 combined give ~3-day optical revisit at 10-30 m resolution.
Geostationary satellites sacrifice spatial resolution for temporal cadence (minutes).
Commercial constellations (Planet, Maxar) fill the high-resolution, high-cadence niche.
Lidar (ICESat-2) and gravity (GRACE-FO) provide unique 3D and mass change measurements.