Recommendations from the 2022 NASA workshop

Reference: Advancements in Satellite Observations of Inland and Coastal Waters: Building Towards a Global Validation Network by Avouris et al 2026. Remote Sens. 2025, 17(24), 4008; https://doi.org/10.3390/rs17244008

A NASA Workshop on the Validation of Satellite-derived Optical and Water Quality Parameters for Coastal and Inland Waters was held at the University of Wisconsin-Madison, June 7-9, 2022. Several recommendations emerged from the workshop on validation needs. These suggestions are directed at agencies and institutions for consideration in support of future planning efforts.

Key Recommendation #1 – Validation in understudied regions

We have shown that 55% of validation studies are performed in the US and China. As such, there is a need for more global representation of validation studies, which is probably linked to funding availability, lack of adequate training, equipment, or different scientific priorities. Some regions are particularly underrepresented, including Latin America and the Caribbean, and Africa. We highlight the need for support to conduct studies in these regions

Key Recommendation #2 – Educational resources

Provide multilingual educational resources for end-users so they can learn how satellite-derived products were created and their potential applications and limitations. Educational materials should also be provided in a variety of formats to account for differences in end-user capabilities (remote sensing experts and non-experts).
Provide multilingual hands-on training for water quality professionals and volunteers to expand data collection and support training on the use of satellite-derived data for water quality management.

Key Recommendation #3 – Protocol development 1066

Translate protocols and standard operating procedures to languages other than English to promote the dissemination of the content.
Consider specific characteristics (e.g. optically shallow waters) when developing and/or adapting available (open ocean) protocols for measurements in inland and coastal waters.
Collect matched data pairs of in situ reflectance and water quality attributes to help improve algorithm and model development, including the revision of implicit assumptions of open ocean models that are often adapted to inland or coastal waters.
Record and report validation measurement metadata in a standardized format, including at least the following information: latitude, longitude, date/time, Secchi depth, water depth, elevation, wind conditions, cloud cover, and water temperature. It is also desirable to record the methods used for data collection and processing, including sensor manufacturer and model when applicable.
Consider the appropriate sampling time-windows before and after satellite data acquisition for inland and coastal waters. The development of a time-window guide considering different characteristics of the water bodies would be very useful when designing validation sampling plans. Parameters that may be important to consider when developing a time-window guide include: tidal range (coastal waters) or mean residence time (inland waters), diurnal variability; spatial variability (homogeneous or heterogeneous); spatial resolution of the satellite sensor; and sampling accessibility.
Develop standard operating procedures to account for uncertainty and environmental variability of measurements. This could include but is not limited to: replication of measurements or samples over a short period of time (in the scale of minutes) to reduce and account for random errors; and report, at least, simple uncertainty quantifications, such as standard deviation, percentiles, and number of samples.

Key Recommendation #4 – Data uncertainty and expectations

Clearly communicate uncertainties associated with both field measurements and satellite data products.
Identify the conditions or regions for which a satellite data product is expected to perform well or poorly.
Focus on understanding and defining which uncertainties are “acceptable” across dynamic systems through improving the understanding of end-user needs.

Key Recommendation #5 – Further research

Further research on the severity of the impacts of known issues (e.g., adjacency effects, shading and reflectance from the deployment platform) on water quality attribute retrievals and radiometric measurements for inland and coastal waters.
Further research on atmospheric correction for coastal and inland waters, including: the validation of available atmospheric correction procedures across varying atmospheric and water column states to ensure robustness, the development of atmospheric corrections for inland and coastal waters that implicitly account for straylight from land adjacent pixels, and to this end, generating validation data sets impacted by adjacency effects so that tools can be generated to further address the issue.
Studying the effects of particle size (algal and non-algal), composition of dissolved and particulate matter, and algal community composition and pigments on the absorption and scattering properties of inland and coastal water bodies (i.e., on the IOPs) to better understand their effects on aquatic reflectance.
Further research to improve in situ absorption and scattering sensor designs or develop corrections for existing sensors that work well in highly attenuating/scattering mediums, which are often common in inland/coastal waters and incorporate these measurements in field campaigns.
Further research on the characterization of known interferences and issues (e.g., NPQ, temperature quenching, etc.) with in situ fluorometry-based sensors (e.g. Chl a, CDOM, accessory algal pigments) to expand their use as satellite validation data.