Figure 1. NRCS Walnut Gulch SCAN site in Arizona, USA (Courtesy NSIDC)

About the SMEX04 North American Monsoon Experiment (NAME)

The parameters of the Soil Moisture Experiment 2004 (SMEX04) campaign were based on, and integrated with, the complimentary objectives of the North American Monsoon Experiment (NAME), namely the development and evaluation of remotely sensed land surface products for terrestrial hydrology.

One hypothesis of NAME is that soil moisture in the southwestern United States and northern Mexico is a land surface boundary condition that controls the onset and intensity of the North American Monsoon System (NAMS). Among the most important land surface boundary conditions that contribute to NAMS are surface wetness and temperature. Before the SMEX04 NAME campaign, however, few soil moisture observations had been conducted in the southwestern U.S. and none had been conducted in northern Mexico. In addition, precipitation measurements that could be used to derive estimates of surface wetness either did not exist or were inadequate.

As part of ongoing efforts to validate soil moisture products from the AMSR-E instrument, several watershed sites in the U.S. were established to provide continuous long-term observations of surface soil moisture and temperature. One such site is the Walnut Gulch Watershed near Tombstone, Arizona USA. For SMEX04 NAME, an in situ soil moisture network was also established in the Sonora region of Mexico. The SMEX04 NAME region encompassed heterogeneous topography and variety of arid to semiarid surface conditions. The terrain between these regional study areas, from Tombstone, Arizona to Hermosillo, Mexico, varies from flat desert to mountains with elevations of more than 2500 meters. Owing to the relatively sparse vegetation of these study regions, as compared to other SMEX study regions, SMEX04 NAME provided ideal conditions under which to evaluate AMSR-E soil moisture products (Remote Sensing of Environment 2008). For example, Cosh et al. addressed soil moisture network validation and concluded that the SMEX04 NAME network provided highly accurate (approximately 0.01 m’/m’) estimates of the watershed average.

In addition to SMEX04 NAME data, additional and on-going measurements of soil moisture and associated parameters are available at the Southwest Research Center's (SWRC) Web site. These complimentary data inform continued NAME science investigations and build upon our understanding of important land surface features and how new technologies will benefit soil moisture mapping in the future.

The photographs in Figures 1 and 2 show members of the Arizona Walnut Gulch sampling team and the United States Department of Agriculture (USDA) Soil Climate Analysis Network (SCAN) site at Lucky Hills, Arizona USA. Figure 3 is a Landsat 5 image showing the Arizona Walnut Gulch and Mexico Sonora regional study areas.

To view data and documentation, see SMEX04 Data Sets.

Figure 2. Arizona Walnut Gulch Sampling Team at the Tombstone Laboratory

Figure 3. SMEX04 North American Monsoon Experiment Regions
False color Landsat 5 image from 8 June 1997. The yellow boxes indicate the SMEX04 NAME regional study areas; the top box indicates the Arizona Walnut Gulch Region and the bottom box indicates the Mexico Sonora Region. (Courtesy USDA Hydrology & Remote Sensing Laboratory)