9 Cross-Sensor Harmonization¶

Last updated: May 5, 2025

Applies to: Landsat Collection 2 Level-2 Tier 1 Surface Reflectance (SR) and Collection 2 Tier-1 Top-of-Atmosphere (TOA) products in the Climate Engine App and API

Summary¶

Climate Engine does not apply additional cross-sensor harmonization when you request spectral or thermal bands, NDVI, EVI, or other band-based metrics from Landsat 5, 7, 8, or 9 beyond the corrections applied to Landsat Collection 2.
The USGS Collection 2 processing pipeline already standardizes radiometry, geometry, and per-scene quality so that comparisons across sensors are considered analysis-ready for most applications.
Published guidance from Google Earth Engine (GEE) and the USGS Landsat team indicates that standardized harmonization coefficients have not been produced for Collection 2 and are likely unnecessary.

Why doesn't Climate Engine harmonize Landsat sensors?¶

Collection 2 is generally considered analysis-ready.

The USGS reprocessed the entire Landsat archive using similar atmospheric-correction models: LaSRC for optical SR for OLI and LEDAPS for TM and ETM+.
From USGS: "Landsat scenes with the highest available data quality are placed into Tier 1 and are considered suitable for time-series analysis."
Level-2 SR products are delivered in the same spatial grid (30 m), using the same metadata structure and Quality Assessment (QA) bits.
From USGS: "Landsat Collection 2 Level-2 Science Products are time-series observational data processed for consistency and continuity to measure effects of environmental change and serve as input into Landsat essential climate variable Level-3 Science Products."

Guidance and lack of evidence for the need for additional harmonization.

Earth Engine's FAQ on cross-sensor surface reflectance states that additional harmonization is usually unnecessary.
That FAQ also notes that while Roy et al. (2016) analyzed reflectance differences between Landsat 7 and 8, similar standardized Collection 2 harmonization coefficients have not been broadly established.

Practical experience using Landsat Collection 2

In practice, you may notice small differences in surface reflectance between Landsat 5 and 7 for overlapping periods (1999-2001), and between Landsat 5 and Landsat 8/9 eras.
In our experience, those differences are generally small and most noticeable in sparse vegetation or bright-background environments such as desert landscapes where NDVI is very low.

Related dataset pages:

Frequently Asked Questions¶

Q1. Does Collection 2 harmonize TOA products too?¶

Yes. Collection 2 Tier-1 TOA reflectance and radiance are radiometrically recalibrated using updated gain/bias tables. However, TOA values are still influenced by atmosphere, so we generally recommend SR for biophysical indices.

Q2. Is harmonization different across indices?¶

No. All indices are computed from the same spectral bands. Any residual cross-sensor bias in band reflectance will tend to propagate into derived indices as well.

Q3. What about Landsat 1-4 MSS or Collection 1 data?¶

Older missions and previous collections were not processed with the same algorithms. Cross-sensor calibration is more complicated in those cases and is not covered by this FAQ. Climate Engine does not currently provide MSS data, and Collection 1 has been superseded by Collection 2.