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Choose Sentinel-3 for oceans, broad-area environmental conditions, sea or land-surface temperature, fire context, vegetation status at regional scale, and surface-height measurements. Choose Sentinel-2 when you need fine-detail optical imagery of land and vegetation. Choose Landsat when a long, consistent archive, 30 m multispectral data, or thermal observations matter. Sentinel-2 and Landsat can be combined for denser land time series; Sentinel-3 usually complements them because its pixels are much larger.
Fast answer: match the satellite to the question
The three missions overlap in broad environmental monitoring, but they are designed around different measurement scales and instruments. Start with the variable you need, then check pixel size, revisit geometry, clouds, product level, and the dates covered by the mission.
| Main requirement | Best starting point | Why it fits | Important check |
|---|---|---|---|
| Ocean colour, chlorophyll-related optical products, sea-surface temperature, sea-surface height, or broad marine monitoring | Sentinel-3 | Its OLCI, SLSTR, and SRAL instruments are dedicated to ocean and large-scale environmental measurements. | Select the correct instrument and processing level; the spatial sampling is too coarse for many small coastal or inland features. |
| Frequent, detailed optical mapping of fields, forests, wetlands, or built-up land | Sentinel-2 | It provides 13 optical bands, a 10 m headline resolution, and a five-day two-satellite equatorial revisit. | Resolution differs by band, and clouds can remove otherwise scheduled observations. |
| Long-run land-change analysis, multispectral mapping, or land-surface temperature | Landsat 8/9 and the Landsat archive | Landsat supplies a decades-long program, 30 m multispectral imagery, and thermal measurements from TIRS. | Choose the appropriate historical mission, Collection 2 product, and processing level. |
| More frequent medium-resolution land observations | Sentinel-2 plus Landsat | Their acquisition schedules can fill gaps when the analysis is harmonized carefully. | Band definitions, calibration, viewing geometry, clouds, and time period must be compatible. |
| Regional land status or rapid fire and temperature context alongside detailed imagery | Sentinel-3 plus Sentinel-2 or Landsat | Sentinel-3 supplies broad, frequent context while the other mission resolves smaller features. | Do not interpret a Sentinel-3 pixel as if it represented a small parcel or individual object. |
What each mission actually measures
Sentinel-3: a multi-sensor environmental mission
Sentinel-3 is built to measure large-scale changes in oceans, land, ice, and the atmosphere rather than to act as a very-high-detail land camera. Its instruments and product families are described by the European Space Agency (ESA).
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- SLSTR (Sea and Land Surface Temperature Radiometer): visible, near-infrared, and shortwave-infrared channels at 500 m; thermal-infrared channels at 1 km. It measures sea- and land-surface temperature and includes channels useful for fire monitoring.
- SRAL (Synthetic Aperture Radar Altimeter): measures sea-surface and other surface heights. Its equatorial ground-track spacing is 47 km after a 27-day repeat period, so it is not a substitute for a fine-grid optical image.
ESA gives approximate ocean revisit values of one day for SLSTR and two days for OLCI with the two-satellite constellation. The broad swath is what makes Sentinel-3 useful for regional and global dynamics, but that same sampling limits its ability to resolve narrow rivers, small fields, individual buildings, or small burn scars.
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Sentinel-3 products include separate SLSTR, OLCI, and SRAL chains plus combined OLCI/SLSTR products for ocean colour, land reflectance, temperature, topography, and vegetation. ESA says core products are typically available within three hours of sensing; actual availability depends on the product and processing level. Review the current catalogue on ESA’s Sentinel-3 data-products page before designing an automated workflow.
Sentinel-2: detailed optical land observation
Sentinel-2 is the fine-detail optical option in this comparison. ESA lists 13 multispectral bands, a 290 km swath, a 10 m headline resolution, and a five-day revisit at the equator for the two-satellite constellation. The mission description is available on ESA’s Sentinel-2 page.
The 10 m number is a headline specification, not the sampling of every band. Before calculating an index or training a classifier, check the resolution of each band in the product you selected and resample only with a method appropriate to the analysis. Sentinel-2C joined the mission after its launch on 5 September 2024.
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ESA states that the constellation revisits the equator every five days and revisits more frequently at higher latitudes. ESA and NASA have also described coordination with Landsat 8 as aiming for an average three-day revisit over the equator for comparable products. That is a coordination goal, not a promise that every location will receive a usable, cloud-free image every three days; orbit geometry, clouds, acquisition plans, and product availability still control what you can use.
Landsat: the long archive and thermal record
Landsat is the choice when historical consistency, medium-resolution multispectral data, or thermal measurements are central. On Landsat 8, the Operational Land Imager (OLI) provides 15 m panchromatic and 30 m multispectral imagery across a 185 km swath. The Thermal Infrared Sensor (TIRS) measures land-surface temperature in two thermal bands. See the current specifications on the USGS Landsat 8 mission page.
Landsat 8 and Landsat 9 each image the Earth on a 16-day cycle and are offset by eight days, providing an eight-day interval between the two satellites for locations that are acquired. Those are nominal acquisition cycles, not guarantees of a clear observation. The USGS Landsat Acquisition page says Level-1 products are available for download within six hours of acquisition; timing for other products and processing stages can differ.
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For analysis-ready surface variables, USGS provides Collection 2 Level-2 surface-reflectance and surface-temperature products. Generation timing, known issues, and reprocessing details vary by product, so consult the Collection 2 Level-2 documentation for the exact product you intend to use.
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Specifications side by side
| Characteristic | Sentinel-3 | Sentinel-2 | Landsat 8/9 |
|---|---|---|---|
| Primary role | Large-scale ocean, land, ice, atmosphere, temperature, fire, colour, vegetation, and height monitoring | Multispectral optical land and vegetation observation | Long-term multispectral land record plus thermal measurements |
| Key instruments | OLCI, SLSTR, SRAL | Multispectral Instrument (13 bands) | OLI and TIRS on Landsat 8; corresponding sensors on Landsat 9 |
| Optical or multispectral detail | OLCI: 300 m; SLSTR: 500 m visible/NIR/SWIR | 10 m headline resolution; other bands have different resolutions | 30 m multispectral; 15 m panchromatic |
| Thermal detail | SLSTR thermal infrared: 1 km | No thermal-infrared band in the mission’s optical instrument | TIRS measures surface temperature in two thermal bands |
| Swath | OLCI: 1,270 km | 290 km | 185 km on Landsat 8 |
| Nominal revisit or acquisition cycle | OLCI about two days globally; SLSTR about one day over oceans for the two-satellite constellation | Five days at the equator for the two-satellite constellation; faster at higher latitudes | Each of Landsat 8 and 9: 16 days; eight-day offset between them |
| Typical product timing stated by the operator | Core products typically within three hours of sensing | Not stated as one universal interval; depends on product and processing | Level-1 download within six hours of acquisition; other products vary |
| Public access | Copernicus Data Space, linked from ESA mission information | Copernicus data services | USGS no-cost open data policy and download services |
These are mission and instrument specifications, not a controlled accuracy comparison. A lower pixel size does not automatically mean a better result: the correct choice depends on the variable, scale, cloud conditions, archive length, and processing method.
Choose by the question you need to answer
Ocean colour, water quality, or marine conditions
Begin with Sentinel-3 when the target is ocean colour, broad water properties, sea-surface temperature, or sea-surface height. OLCI’s 21 bands and 1,270 km swath support systematic coverage, while SLSTR supplies temperature observations. SRAL is the relevant instrument for height measurements. Select the product that represents the variable you will model rather than downloading a generic image and attempting to derive an unsupported quantity.
For a small estuary, narrow coastal plume, or individual lake, evaluate the pixel size before committing. A 300 m OLCI pixel can mix land, shallow water, and open water; a 1 km thermal pixel can mix several surface types. Sentinel-2 may be more useful for detailed shoreline and small-waterbody mapping, although it does not provide Sentinel-3’s dedicated thermal and altimetry capabilities.
Vegetation, crops, forests, and land cover
Use Sentinel-2 when you need to distinguish fields, forest stands, roads, clearings, or other features at approximately 10 m scale and the necessary information is represented in its optical bands. Its 13-band design supports many vegetation and land-cover workflows, but cloud screening and band-specific resolution remain part of the method.
Use Landsat when the question extends far back in time, when a 30 m multispectral record is sufficient, or when thermal information is required. For regional vegetation status, drought context, or broad fire effects, Sentinel-3 can add frequent wide-area observations. It should be treated as regional context, not as a replacement for parcel-scale imagery.
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Fire detection and burn assessment
Sentinel-3’s SLSTR includes shortwave- and thermal-infrared channels useful for rapid, broad fire and temperature context. Its coarse pixels are well suited to regional screening and situational awareness, but they can miss or dilute small fires. Sentinel-2 or Landsat can then provide finer optical evidence of burn perimeters and land-cover change when cloud-free acquisitions are available. Match the acquisition time to the event: a frequent nominal revisit is valuable only if the satellite actually observed the location and the product is usable.
Land-surface temperature
Choose Landsat when you need thermal measurements at its mission’s medium spatial scale and want to connect them to a long land record. Sentinel-3 SLSTR provides more frequent, broad-area temperature observations, but its thermal sampling is 1 km. That makes it appropriate for regional patterns and large homogeneous surfaces, not for a small urban lot or narrow agricultural plot. Sentinel-2 can supply detailed optical context but does not replace a thermal sensor.
Surface height and topography-related ocean measurements
Sentinel-3’s SRAL is the relevant instrument for sea-surface and other surface-height products. Neither Sentinel-2’s optical bands nor Landsat’s ordinary multispectral imagery provides an equivalent altimetry measurement. SRAL’s 47 km equatorial ground-track spacing after 27 days means that users must design around tracks and repeat periods rather than expect a wall-to-wall image on every revisit.
Understand resolution, revisit, and usable observations
Spatial resolution is not the same as feature accuracy
A pixel is a sampling unit, not a guarantee that every object inside it can be identified. Sentinel-3’s 300 m OLCI and 500 m or 1 km SLSTR samples can contain several land covers. If the target is smaller than the pixel or changes sharply within it, the measured value is a mixture. Sentinel-2’s 10 m headline figure and Landsat’s 30 m multispectral sampling are generally more appropriate for local land features, subject to band resolution, geolocation, atmospheric effects, and cloud contamination.
Nominal revisit is not a cloud-free schedule
Sentinel-2’s five-day equatorial revisit, Sentinel-3’s approximate one- or two-day values for specific instruments, and Landsat’s eight-day combined acquisition interval describe orbit and constellation opportunities. A usable time series also depends on whether the site was acquired, whether clouds or haze obscure it, whether the sun and viewing geometry are suitable, and whether the desired processing level has been generated.
Swath width affects coverage and edge effects
Sentinel-3’s 1,270 km OLCI swath enables broad, systematic coverage. Sentinel-2’s 290 km and Landsat’s 185 km swaths cover less area per pass but provide finer sampling. When comparing scenes at tile or path-and-row boundaries, preserve the acquisition geometry and avoid treating scenes from different viewing angles as identical observations.
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A practical selection and download workflow
- Define the variable and feature size. Write down whether you need reflectance, a vegetation indicator, ocean colour, surface temperature, fire context, or surface height. Record the smallest feature that must be resolved.
- Choose the mission family. Start with Sentinel-3 for broad environmental variables and height; Sentinel-2 for detailed optical land work; Landsat for the long archive, 30 m multispectral observations, or thermal measurements.
- Select the instrument and product. For Sentinel-3, distinguish OLCI, SLSTR, SRAL, and combined products. For Landsat, distinguish Level-1 from Collection 2 Level-2 surface-reflectance or surface-temperature products. For Sentinel-2, verify the bands and their native resolution.
- Set the time and cloud requirements. Treat revisit as an opportunity window. Search a date range wide enough to account for clouds, and apply a documented cloud and quality mask rather than assuming the nominal interval is usable.
- Check acquisition geometry and scale. Confirm that the swath, orbit or track, pixel size, and viewing angle fit the site. For Sentinel-3, test whether mixed pixels make the target unusable before building a model.
- Use the operator’s access service. ESA points Sentinel-3 users to Copernicus Data Space through its Sentinel-3 facts and figures page. Landsat data remain available under the USGS no-cost open data policy; search and download options are described at USGS Landsat Data Access.
- Document processing choices. Save the mission, sensor, collection, product level, acquisition date, coordinate reference system, resampling method, cloud mask, and calibration version with every analysis.
How to combine Sentinel-2 and Landsat responsibly
Combining Sentinel-2 and Landsat can increase the number of observations available for land monitoring, but the sensors are not interchangeable by default. Their bands have different spectral response functions, pixel sizes, viewing geometries, calibration histories, and cloud conditions. An eight-day Landsat 8/9 interval and a five-day Sentinel-2 constellation interval also do not guarantee synchronized, cloud-free scenes.
- Use surface-reflectance products produced for comparable atmospheric and radiometric purposes.
- Map each variable to bands that are genuinely comparable; do not assume similarly named bands have identical spectral responses.
- Choose a common grid and state which sensor is aggregated or resampled.
- Preserve acquisition dates and viewing angles so a model can account for temporal and geometric differences.
- Validate the combined series for the specific landscape and period; mission summaries do not establish a universal cross-calibration workflow.
A sensible pattern is to use Sentinel-2 for fine spatial detail, Landsat for historical continuity and thermal measurements, and Sentinel-3 as a broad-scale environmental or temperature layer. Whether that combination improves a result must be demonstrated for the variable and study area rather than assumed from revisit numbers alone.
Common mistakes and how to avoid them
Using Sentinel-3 for a small parcel
If the target is smaller than a 300 m OLCI or 1 km SLSTR sample, the pixel may be dominated by surrounding surfaces. Move to Sentinel-2 or Landsat when the task requires parcel, road, building, or small-waterbody detail.
Treating every Sentinel-2 band as 10 m
The 10 m value is a headline mission specification. Check the native resolution of each band and the product’s resampling before calculating indices or comparing bands.
Calling a revisit interval a guaranteed observation
Orbit cadence does not remove clouds, haze, missing acquisitions, or product-generation delays. Build a date window and quality-control step into the workflow.
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Level-1 radiance or reflectance products, surface-reflectance products, and surface-temperature products have different corrections and intended uses. Keep the product level and processing generation explicit in file names and metadata.
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Combining readings without checking scale
Do not average a 1 km thermal pixel with a 10 m optical pixel and call the result a single-resolution measurement without defining the aggregation. Match the spatial support of the statistic to the question.
Assuming access and latency are identical
Sentinel-3 core products are typically available within three hours according to ESA, while USGS states that Landsat Level-1 products are available within six hours of acquisition. Those statements apply to the specified products and do not establish identical timing for every collection, processing stage, or Sentinel-2 product.
Current mission status and access notes
ESA lists Sentinel-2C as having joined the Sentinel-2 mission after its 5 September 2024 launch. ESA also lists Sentinel-3C as launched on 15 September 2026 on its current mission information. Because constellation membership and operational status can change, verify the live mission pages before making a time-critical acquisition plan.
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Bottom line
Use Sentinel-3 when the value of wide swath, frequent coverage, ocean and land-surface temperature, fire context, ocean colour, vegetation status at regional scale, or surface height outweighs the need for fine detail. Use Sentinel-2 for detailed optical land and vegetation mapping. Use Landsat for the long historical record, 30 m multispectral observations, and thermal measurements. For many land-monitoring projects, Sentinel-2 and Landsat form the detailed time series while Sentinel-3 supplies the broad environmental context.
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