Aerial Measurement of Snow Water Equivalent by Terrestrial Gamma Radiation Survey

Abstract

Research studies measuring terrestrial gamma radiation from aircraft to determine snowpack water equivalent are reported. Both spectral and total count data were collected using 10·16 em by 10·16 em (4 in.) NaI (T1) scintillation crystals. Extensive ground truth data were used in conjunction with count rates obtained to develop empirical procedures relating count attenuation with snow water equivalent. Soil moisture, altitude, and air density corrections were made in the course of development of the method. Spectral relations are compared with theoretical. Significant limitations on data collection and interpretation imposed by the presence of radon gas are discussed. Because of radon gas interference in the total count, the spectral method gives the best measurement of water equivalent in the snow-flood sensitive North-Central United States. RESUMEOn rend compte des etudes faites en vue d'evaluer, a partir d'un avion, la radiation gamma terrestre et pour determiner la hauteur d'eau equivalente des couches de neige. Les donnees spectrales ainsi que les donnees de calcul total ont ete recueillies au moyen de cristaux de scintillation de 10·16 em sur 10·16 em (4 in.) NaI(Tl). Des donnees etendues sur la verite terrestre furent utilisees de concert avec les taux de calculs obtenus pour developper les processus empiriques qui ont un rapport entre I'attenuation et la hauteur equivalente d'eau de neige. Des corrections sur I'humidite du sol, l'altitude et la densite de I 'air ont ete faites au cours du developpement de la methode et les rapports spectraux ont ete compares aux rapports theoriques. On discuta des limitations significatives sur la collection et I'interpretation des donnees imposees par la presence du gaz radon. A cause de l'intervention du gaz radon dans Ie calcul total, la methodespectrale fournit la meilleure evaluation de la hauteur d'eau equivalente dans le Nord et le Centre des Etats-Unis qui sont sujets aux crues des neiges. .

The Difficulties of Measuring the Water Saturation and Porosity of Snow

“…Methods currently in use to determine the water equivalent of snow include terrestrial gamma-ray surveys (Peck and Bissell, 1973) and nuclear profiling gages. The use of nuclear sources which are attenuated by the snow was introduced by Gerdel and others (1950) and refined by Smith (e.g.…”

Hydrometeorology

“…Approximately 13 years ago, I presented a paper at the Western Snow Conference entitled "The Little Used Third Dimension" (Peck, 1964). The title was intended to indicate that hydrologists were not making maximum use of meteorological measurements to help determine the distribution of precipitation in mountainous areas.…”

“…Other uses of satellite imagery are also being applied in routine hydrologic forecasting, such as determining the extent of the snow cover for seasonal water supply and snowmelt flood forecasts. No adequate method has been developed for measuring from space the water equivalent of the snow cover, but techniques using low-flying aircraft measuring the natural gamma radiation of the earth are being used (Peck and Bissell, 1973).…”

Investigating the potentialities of Monte Carlo simulation for assessing soil water content via proximal gamma-ray spectroscopy

“…As water has 1.11 times as many electrons per gram compared to most soils, water is 1.11 times as effective in attenuating gamma-radiation compared to typical soils (Grasty, 1997). The expected high sensitivity of gamma spectroscopy to soil water content has triggered numerous studies which addressed a broad range of applications including soil classification (Beamish, 2013(Beamish, , 2014, radon flux mapping (Manohar et al, 2013;Szegvary et al, 2007) and snow water equivalent assessment (Carroll and Carroll, 1989;Peck and Bissell, 1973). Nevertheless, the potentialities of the method for monitoring soil moisture dynamics have been not fully explored yet (Bogena et al, 2015;Pereira, 2011), especially in the field of proximal sensing, which is foreseen to be an efficient strategy for filling the existing gap between punctual measurements, generally provided by in situ electromagnetic sensors (Walker et al, 2004), and remote measurements, typically performed by satellites (Brocca et al, 2017;Zeng et al, 2016).…”