Technical Abstract: The Earth Observing System (EOS) instrument teams must validate the operational products they produce from the Terra spacecraft data. As a pilot for future validation activities, four EOS teams (MODIS, MISR, ASTER, and Landsat-7) and community experts conducted an 11-day field campaign in May 1997 near Las Cruces, NM. The goals of the Prototype Validation Exercise (PROVE) included (1) gaining experience in the collection and use of field data for EOS product validation; (2) developing coordination, measurement, and data-archiving protocols; and (3) compiling a synoptic land and atmosphere data set for testing algorithms. PROVE was held at the USDA-Agricultural Research Service's (ARS) Jornada Experimental Range, an expansive desert plateau hosting a complex mosaic of grasses and shrubs. Most macroscopic variables affecting the radiation environment were measured with ground, air-borne (including AVIRIS and laser altimeter), and dspace-borne sensors (including AVHRR, Landsat TM, SPOT, POLDER, and GOES). Primary successes included the rapid campaign formulation and execution, measurement protocol development, and the significant collection, reduction, and sharing of data among participants.