Attached is a whitepaper that covers both a spatial and temporal validation of Planet’s latest Soil Water Content product.
The paper, which is partly based on Planet’s own field measurements, does a great job explaining why the validation of soil water content is so challenging. Other interesting topics covered are the number of in-situ measurements you need to get an equivalent of 1 Soil Water Content pixel (spoiler alert, this is 7!) within the same uncertainty and results of many temporal validations showing Pearson correlations up to 0.9.
Please reach out to https://www.planet.com/contact-sales/ with any questions!