Assessment of two methods to monitor wetness to control dust emissions, Owens Dry Lake, California

Abstract

Legally mandated control of blowing dust from 250 km² Owens Dry Lake, eastern California, USA is accomplished by wetting within shallow flooding basins. Monitoring of surface wetness is required to assess dust-control compliance. The cost, scale, heterogeneity and limited access prevent the use of moderate-resolution satellite data (e.g. Landsat Thematic Mapper (TM), 28.5 m, chosen a priori as the monitoring base) for calibrating directly to surface wetness. Instead, calibration and testing employed controlled spectrometry converted to equivalent broadbands of TM as surrogates.

Spectra, photography and surface assessments were obtained from twenty-nine 0.07 m² undisturbed surfaces varying from flooded to dry and emissive. Two competing broadband methods to assess surface wetting were tested with Landsat TM-equivalent data: TM band 5-equivalent reflectance (TMB5) as a surface wetness analogue; and tasseled cap wetness (TCW), calculated using all six TM-equivalent reflectance bands. Five performance criteria were evaluated: (1) progressive ranking, wet to dry; (2) wet and dry at ends of each index’s distribution; (3) no overlap, wet to dry; (4) large separation, moist/protected to dry/dust-emissive; and (5) clear yes/no dichotomy, whether moist/protected or not. For all criteria, TMB5 outperformed TCW. TMB5 reflectance of 0.19 provided an empirically consistent, verifiable threshold: below this, surfaces are sufficiently wet and protected from windborne dust emission.

Acknowledgments

The authors thank the Great Basin Unified Air Pollution Control District, Bishop, California and Ted Schade, its Air Pollution Control Officer for support and interest in studies leading to development of a monitoring system of Owens Lake dust control efforts. The anonymous reviewers are also thanked for their comments.