can you name a couple examples where these measures are stated?

I think each satellite data has to went through validation. Normally, validation is done through in situ measurements. I was one of the participant to collect soil sample for gravimetric soil moisture measurements, in situ SM measurements using theta probe. At the end satellite SM was validated using theta probe, gravimetric and airborne sensor measurements. Based on the daily measurements for about a month, I think conclusion had been made on accuracy. Hope it helps.

Thanks Dr. Ram and Andreas for the responses.

In SMAP and SMOS missions, the expected soil moisture accuracy is 0.04 v/v. I was rather trying to find the base for the numeric value of 0.04 v/v.

Dear Indishe,

Have you had chance to look at SMAP handbook? Please go through page from 48 to 50, section II. Requirements and validation Metrics to get your answer in depth. Please let me know if you want me to attach the handbook.

Thanks

I heard the reply to this question at the satellite soil moisture workshop from the PI of the validation of SMAP.

Soil moisture range is about 0.4 vol/vol. 10% error is acceptable. Therefore, 0.04 vol/vol should be the target.

Note also that for SMAP it is unbiased RMSE, for SMOS RMSE. The SMAP requirement is more appropriate.

Thanks Dr. Luca for the clarification. That's a fair explanation.

Thanks Dr. Ram.