P.I.(s): Eugene L. Peck -- Hydex Corp; Tom Carroll -- NWS NOAA
Objectives: This project utilizes airborne gamma sensing to measure soil moisture (SM) in areas underlain by permafrost (Northern Study Area) and in forested boreal areas and cooperated with HYD-4 in the measurement of Snow Water Equivalent (SWE). Estimates of the water content in the Moss/Humus layers, where those layers are significant, were also obtained. The airborne estimates of SWE and SM are being used with estimates from other investigators to prepare information about the distribution of SWE and SM for the BOREAS sites and to investigate the relationships of the site measurements to those observed on a regional scale. Inter-comparison studies of estimates of SWE and SM by the airborne gamma and other remote sensing techniques are being conducted.
Flight lines, representing the different vegetative covers for the areas, have been established in the Northern Study Area (NSA), in the Southern Study Area (SSA), and along transects between the tow areas. The flight lines are primarily along roads due to accessibility constraints for the collection of ground truth data for calibration purposes. Background flights and in situ soil moisture measurements were obtained for calibration of some of the flight lines during September 1993. Airborne snow measurements were flown using the airborne gamma system for snow course and soil moisture measurementes during February 1994 (HYD-4). Airborne soil moisture measurements and measurements of the water content of the Moss/Humus layer were collected during IFC-2 and IFC-3.
View a special paper on "High Cosmic Radiation in the SSA" by Dr. Gene Peck.
The objectives of this study are: 1) to obtain improved estimates of the soil moisture (SM) of the mineral soil, 2) to develop techniques for measuring the water content (WC) of the moss/humus layer, 3) to provide assistance to HYD-4 in measuring the water equivalent (WE) of the snow cover, 4) to provide information on temporal and spatial variations in the SM and of the WC of the moss/humus layer.
Data Collected and Equipment Used:
The National Weather Service, NOAA, airborne detector package is used to collect airborne radiation, temperature, pressure, and aircraft altitude data over selected flight lines for providing airborne estimates of the SM and of the WC of the moss/humus layer.
Airborne soil moisture measurements are based on the difference between the measured natural terrestrial gamma radiation flux for comparatively wet and dry soils. Over 800 in situ ground measurements of the SM, the WC of the moss/humus layer, and of the soil and vegetative cover were collected for calibration purposes.
Places and Times of Measurements:
Airborne gamma ray surveys were flown for 48 BOREAS flight lines during IFC-W (February 1994), and during IFC-2 and IFC-3 n the summer of 1994. Surveys over the BOREAS Northern Study Area (NSA) and along transect lines between the NSA and SSA were collected only a few times for calibration of the flight lines in support of the snow survey program of HYD-4. In situ soil moisture measurements were collected once for most flight lines for calibration of the natural terrestrial radioisotope signal. Airborne surveys were flown over the SSA for consecutive days during IFC-2 and IFC-3.
The airborne measurement of the SM and WC is not reliable for extremely wet areas. The ground measurements for calibration of the flight lines must be representative of average conditions.
Observed High Cosmic Radiation: The airborne radiation measurements include a measure of incoming cosmic radiation. Only during three days in September 1994 were high energy cosmic rays measured (considered as a rare event) that may have importance for other BOREAS radiation measurements.
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Last Updated: October 21, 1997