Boreas Data Documentor Appendix 3 - Shewchuk, S.R. 1996. The Mesoscale Distribution of Soil Moisture over the SRC/NASA Mesonet Sites for the IFC 2 Periods of 1994. Draft. Saskatchewan Research Council (SRC) Pbu. No. R-1570-1-D-96, SRC, Saskatoon, Saskatchewan. This is in WordPerfect 6.1 format. The Mesoscale Distribution of Soil Moisture over the SRC/NASA Mesonet Sites for the IFC 2 Periods of 1994 by S.R. Shewchuk Atmospheric Sciences Section Environment Branch Resources and Environment Group Saskatchewan Research Council SRC Publication No. R-1570-1-D-96 15 Innovation Blvd. Saskatoon, SK S7N 2X8 Phone: 306-933-5400 Fax: 306-933-7817 May, 1996 TABLE OF CONTENTS page INTRODUCTION 1 METHODS 1 The Sensor 1 Determination of Soil Moisture 4 RESULTS 4 CONCLUSION 8 REFERENCES 8 LIST OF TABLES page Table 1 Soil textural classes for the SRC BOREAS mesonet sites 5 Table 2 Soil parameters at each SRC BOREAS site 5 Table 3 The calculated soil moisture potential (Y) for the IFC 2 period in 1994 6 Table 4 The estimate mean soil moisture (N) for the BOREAS IFC 2 period of 1994 6 LIST OF FIGURES page Figure 1 The heat dissipation matric potential sensor 2 Figure 2 Response of the heat dissipation matrix potential sensor for various water potentials 3 Figure 3 Temperature difference variation at the Old Aspen Prince Albert National Park site during IFC 2 in 1994 7 INTRODUCTION The Saskatchewan Research Council (SRC) has set up the surface atmospheric science mesonet for BOREAS (Shewchuk 1996). Soil moisture within this mesonet is measured with the Heat Dissipation Matric Potential Sensor (Bilskie 1995). This is a new concept sensor for determining soil moisture that SRC was asked to put into the mesonet for BOREAS by NASA. Classical methods of determination of soil moisture with a remote system was with the soil moisture block. The Heat Dissipation Matric Potential Sensor can potentially increase the reliability and accuracy of this measurement over the soil moisture block sensor (Wittrock 1994). METHODS The Sensor The principle behind the heat dissipation matrix potential sensor is simply that, when a constant power is applied, the temperature increase in the vicinity of the heating element is related to the thermal conductivity of the material which, in turn, is dependent on the amount of water present. It is an empirical device in its present usage. Typically, 50 milliamps applied to the heating element for twenty seconds will cause a temperature increase of between 1.5%C and 3%C. See Figure 1 for a schematic of the probe itself and Figure 2 for typical temperature responses for a range of water potentials. The porous ceramic material of the probe will hydraulically equilibrate with surrounding soil. Any time there is a gradient in water potential between the ceramic and the soil, a water flux will occur. The time required to equilibrate depends on the magnitude of the gradient and the hydraulic conductivity of both the ceramic material and the surrounding medium. The hydraulic conductivity is dependent on water potential and it will take longer to equilibrate at lower water potentials. It is important that there be good hydraulic contact between the ceramic material and the soil. Use of the dissipation probe requires a power source which typically comes from the data loggers at each of the SRC mesonet sites. The Matrix Water Potential Sensor consists of a probe inserted axially in a porous cylinder (length 30 mm, diameter 15 mm). The probe consists of a stainless steel tube (length 25 mm, diameter 0.9 mm) in which a heating element and a thermocouple (copper-constant) are embedded. The resistance of the heating element is approximately 34 ohms. The heating element and thermocouple are connected to extension wires. This connection is embedded in an electrical insulating resin (length 2 cm, diameter 1.5 cm). The thermocouple and heating element should be connected to a temperature recording device and power supply. The temperature rise during the first second of heating is mostly affected by the probe itself. Therefore, the temperature rise after the first second of heating is correlated to the water potential. A heating period of 21 seconds allows for maximum heating time while the heat flux stays within the porous block. Figure 1 The heat dissipation matric potential sensor. Figure 2 Response of the heat dissipation matrix potential sensor for various water potentials. The equation developed to calculate soil moisture potential (Y) from probe temperature difference ( T) is: Y=[0.00026 x 104.89 T]10 (1) Campbell Scientific Inc. is continuing their work on this equation (Greene 1994). SRC has placed the heat dissipation probe into all of the mesonet sites. Soil temperature difference readings are taken once per hour and placed into the BORIS (BOREAS Information System) archive. The initial temperature placed in the archive is the probe temperatures one second after the heat is applied and the final temperature is the temperature twenty seconds after heat is applied. These temperature ranges at each SRC BOREAS site have been provided to BORIS for the entire duration of the project. Determination of Soil Moisture Soil moisture is determined from an equation give by Pielke (1984). The equation is: (2) where Ys is the saturated soil potential for the specific soil of interest; Y is the soil moisture potential give by Equation (1); Ns is the soil porosity; and N is the soil moisture. The value of N is the calculated soil moisture for the individual sites. It is determined by first identifying the soil type at each of the SRC BOREAS sites. Then determining the empirical parameters Ys, Ns and b from Equation (2). Then once the time averaged temperature rise for the period is determined at each site, the soil moisture potential (Y) is determined from Equation (1). This publication is meant to be a preliminary assessment of data provided from the SRC/NASA mesonet system and will provide some guidance to future data interpretations from the sensor for the project. RESULTS Table 1 lists the SRC BOREAS mesonet sites within western Canada with their longitude and latitude locators and the soil textural class. These classes were determined from the Soil Landscapes of Canada Guide (Padbury 1996). Table 1 Soil textural classes for the SRC BOREAS mesonet sites. SRC site Longitude (west) Latitude (north) Textural Class La Ronge -105.29 55.13 Loamy sandy Meadow Lake -108.52 54.12 Silty clay Prince Albert Park (SSA-OA) -106.20 53.63 Sandy loam Nipawin (SSA-OJP) -104.69 53.92 Sand Saskatoon (SRC-CRS) -106.60 52.16 Loam Lynn Lake -101.09 56.89 Loamy sand The Pas -101.05 53.97 Loam Nelson House (NSA-OJP) -98.62 55.93 Sand Thompson -97.87 55.80 Clay Flin Flon -101.69 54.67 Sandy Loam *Canada Soil Survey The empirical parameters of Equation (2) for each SRC mesonet site are shown in Table 2 (Pielke 1984). Table 2 Soil parameters at each SRC BOREAS site. SRC site Ys Ns b La Ronge Loamy sandy 9.0 0.410 4.38 Meadow Lake Silty clay 49.0 0.492 10.40 Prince Albert Park (SSA-OA) Sandy loam 21.8 0.435 4.90 Nipawin (SSA-OJP) Sand 12.1 0.395 4.05 Saskatoon (SRC-CRS) Loam 47.8 0.451 5.39 Lynn Lake Loamy sand 9.0 0.410 4.38 The Pas Loam 47.8 0.451 5.39 Nelson House (NSA-OJP) Sand 12.1 0.395 4.05 Thompson Clay 40.5 0.482 11.40 Flin Flon Sandy Loam 21.8 0.435 4.90 where Ys is the saturated moisture potential; Ns soil porosity; b Clapp-Hornberger parameter. Finally, Table 3 shows a mean value of temperature rise for each of the sites during the IFC 2 period of 1994 for BOREAS. The value of T is interpreted from graphs such as Figure 3, which shows the T variation with time, especially at the Old Aspen Prince Albert National Park site. Soil moisture potential (Y) is calculated from Equation (1) (see Table 3) and soil moisture (N) is calculated from Equation (2) (see Table 4). Table 3 The calculated soil moisture potential (Y) for the IFC 2 period in 1994. SRC site T (mean value) (%C) Y (soil moisture potential) La Ronge 1.4 18.2 x 103 Meadow Lake 3.0 12.0 x 1011 Prince Albert Park (SSA-OA) 1.6 13.0 x 104 Nipawin (SSA-OJP) 0.8 20.5 Saskatoon (SRC-CRS) 3.0 12 x 1011 Lynn Lake 1.2 17.7 x 102 The Pas 0.8 20.5 Nelson House (NSA-OJP) 1.2 17.7 x 102 Thompson NA -- Flin Flon 1.2 17.7 x 102 Table 4 The estimate mean soil moisture (N) for the BOREAS IFC 2 period of 1994. SRC site Ns N La Ronge 5.65 0.410 0.07 Meadow Lake 9.98 0.492 0.05 Prince Albert Park (SSA-OA) 0.589 0.435 0.74 Nipawin (SSA-OJP) 1.14 0.395 0.35 Saskatoon (SRC-CRS) 85.9 0.451 0.01 Lynn Lake 3.25 0.410 0.13 The Pas 0.852 0.451 0.53 Nelson House (NSA-OJP) 3.42 0.395 0.11 Thompson -- -- -- Flin Flon 2.45 0.435 0.18 Figure 3 Temperature difference variation at the Old Aspen Prince Albert National Park site during IFC 2 in 1994. CONCLUSION Soil moisture during the IFC period 7/19 to 8/8 is calculated to range from 7 to 72 percent with the lowest soil moisture being associated with the sandy and loamy sandy areas and the highest soil moisture clay and clay loamy soils. The data that is present in the BORIS archive is only temperature difference between the heated and the unheated probes. John Norman (1996) has recommended that BOREAS principle investigators who use the SRC data file for soil moisture in BOREAS, simply use the soil moisture potential Equation (1) for the individual location of interest and couple this with soil type then calculate the soil moisture during the time period of interest. Since it can only be considered a preliminary assessment, it is recommended that a detailed study be conducted of results of soil moisture from the SRC system and the various soil moisture values collected by the various science teams within the project be assessed. REFERENCES Bilskie, J. 1995. 229 Heat Dissipation Soil Water Potential Probe. Campbell Scientific Inc., 815W. 1800N. Logan, Utah. Greene, J. 1994. Personal communication. Campbell Scientific Inc., Logan, Utah. Padbury, G. 1996. Personal communication. University of Saskatchewan, Saskatoon, Saskatchewan. Pielke, R.A. 1984. Mesoscale Meteorological Modelling. Academic Press. 394 pp. Norman, J. 1996. Personal communication. University of Wisconsin, Madison Wisconsin. Shewchuk, S.R. 1996. Surface mesoscale meteorological system for BOREAS. Presented at the 22nd Conference on Agriculture and Forest Meteorology, 28 January - 2 February, 1996. Atlanta, GA, by the AMS. Wittrock, V. 1994. Examination of the matrix water potential sensor. Saskatchewan Research Council (SRC), Saskatoon, Saskatchewan. SRC Publication No. E-2310-4-E-94. 17 pp. AFM07_SoilMoist.doc Page 1 of 12 The Mesoscale Distribution of Soil Moisture over the SRC/NASA Mesonet Sites for the IFC 2 Periods of 1994 SRC Publication No. R-1570-1-D-96 page 12 The Mesoscale Distribution of Soil Moisture over the SRC/NASA Mesonet Sites for the IFC 2 Periods of 1994 SRC Publication No. R-1570-1-D-96 page 1