do you mean remote sensing?

 Yes, remote sensing too.

NASA has a SMAP project on the retrieval of soil moisture through remote sensing techniques, please refer to the attached link, hope it helps.

https://www.researchgate.net/publication/224136559_The_Soil_Moisture_Active_and_Passive_%28SMAP%29_mission

Article The Soil Moisture Active and Passive (SMAP) mission

Several sensors are available for measuring soil moisture from space (ASCAT, SMOS, SMAP, AMSR-E, AMSR2, ESA CCI, ...). These datasets have nearly daily temporal resolution and 25X25 km space resolution. Many related answers with more details are available on RG (e.g., https://www.researchgate.net/post/which_are_the_better_satellites_for_soil_moisture_studying_in_arid_zones; https://www.researchgate.net/post/How_can_I_get_the_soil_moisture_products_freely_online; ...).

Dear Javed

You can read these papers.

For GPS, see the papers by Kristine Larson: http://spot.colorado.edu/~kristine/Kristine_Larson/Home.html