Proposal submitted to NOAA-CREST
Field Measurement and Verification of Soil Moisture
Data Obtained by a Remotely Sensed Device such as the
Ground Penetrating Radar (GPR)
Dr. Hamed Parsiani, Electrical & Computer Engineering
Dr. Eric Harmsen, Agricultural and Biosystems Engineering
BACKGROUND:
The research work on Remote Sensing Applications for Environmental Assessments and forecasting being conducted by the group of Dr. Hamed Parsiani (under UPRM-CREST) involves Soil Moisture Content Measurements using Ground Penetrating Radar (GPR) and other sensors. The soil moisture determination is essential in the determination of climate change. There are two aspects to this research: one is the use of the GPR equipment and other sensors in obtaining test/field data for soil moisture, and then automatic image processing of the GPR data (images) of large field measurements. The automatic image processing of data is presently underway, which requires learning concepts in image processing, compression, and classification. Algorithms in C-Language, or MatLab, were developed and tested in these areas. The specific areas of concentration have been: image sharpening, noise removal, histogram equalization, restoration of a degraded image, image compression, and image classification. Research work is in progress in this area. The understanding of moisture determination method(s) from the radar reflection coefficients is also in progress.
The first part of this research which requires obtaining test data of known soil types with known characteristics and properties, and measurement of soil moisture in the laboratory using point sensors, presently used by the Agricultural and Biosystems Engineering Department (see attachment), is a necessary first step. The proposal submitted here addresses this need. Dr. Eric Harmsen, as a collaborator, will use his expertise of the soil and the usage of Point Probes and Neutron Probes, and the design of a soil-pit to produce the proper test and field data needed to help properly verify the spatially continuous GPR soil moisture measurements.
INTRODUCTION
Soil moisture content is a critically important parameter used in the analysis of various scientific disciplines. Soil moisture content is an essential parameter in climate change assessments and forecasting, which is the prime emphasis of this collective research. Information about soil moisture content is also important for managing water resources, especially in the area of agricultural water management, in which large quantities of water are used for irrigation. Numerical models for predicting soil water movement are also important in chemical transport studies.
Currently, investigators obtain soil moisture content by intrusive methods, which are limited to point measurements. Interpolation of the point-measured moisture data can lead to errors from interpolation within the nonlinear soil moisture regime. Ground-penetrating radar (GPR) may provide a means of eliminating interpolation error because it can provide spatially continuous estimates of soil moisture in multi-dimensions. In this research, soil moisture data will be obtained using GPR in several Puerto Rican soils, ranging in texture from sand to clay.
OBJECTIVES
This project will cover two-years which coincides with the last two years of the NOAA-CREST grant. During the first year we will focus on gaining familiarity with the GPR unit and deriving accurate measurements from within constructed soil pits. Specifically during the first year the following tasks will be performed:
- Conduct literature review.
- Receive training in application of GPR method
- Construct artificial soil profiles in the UPR Finca Alzamora.
- Analyze soils for physical and chemical characteristics.
- Conduct test of the GPR by comparing its results with traditional soil moisture measurement methods.
- Publish/present first year’s findings.
During the second year, the GPR unit will be used to estimate moisture contents under field conditions. Tests will be conducted at the UPR Experiment Stations at Isabela, Lajas and Fortuna, Puerto Rico. Under field conditions, larger variations in moisture content are expected due to soil layering, textural changes, both horizontally and vertically, and the presences of roots. The selected soils are representative of soil in the tropics, and therefore, may provide information generally applicable to the highly weathered clay soils common among tropical islands.
Specific Objectives for year 2 are:
- Identify field sites for GPR testing
- Install TDR and neutron probe access tubes
- Analyze soils for physical and chemical characteristics.
- Calibrate TDR and neutron probes
- Conduct GPR testing
- Publish/present final results.
PROCEDURE:
This section provides a detailed description of the Year 1 & 2 work tasks.
YEAR 1
Objective 1: A literature search will be conducted to determine the most appropriate frequencies to use for soil moisture measurement in fine textured soils. The literature review will also consider potential problems related to moisture measurement in these soils.
Objective 2: In August, 2002, co-investigators will receive training in the use of the SIR-20 GPR unit from Geophysical Survey Systems, Inc. The data obtained in August will provide sufficient lead time for us to use the GPR before receiving the formal training.
Objective 3: Construct artificial soil profiles in the UPR Finca Alzamora. Artificial soil profiles will be created by excavation of a trench with dimensions 6 m by 1.22 m (see Figure 1). The depth of the trench will vary between 0.6 and 1 meters deep. The pit will be filled with three types of soil (sand, silt and clay), which will be placed into the trench so that mixing of the three soil types is minimized. Figure 1 shows the plan view and vertical cross section of the trench.
Figure 1. Experimental Layout
Objective 4: Soils will be collected from the test pit (several per soil type) for chemical and physical evaluation. Undisturbed samples will be collected from 0 to 25 cm, 25 to 50 cm, 50 to 75 cm and 75 to 100 cm. Soil samples will be analyzed for pH, and electrical conductivity. Other information such as: Point of Zero Net Charge, Anion Exchange Capacity, Cation Exchange Capacity, exchangeable cations, organic C, free iron-alluminiumaluminum oxides, may be obtained. The physical properties that will be determined are texture, conductivity, specific surface of both the soil and the clay fraction, and the soil characteristic curve (suction vs. moisture content). Other information such as aggregate stability, bulk density, porosity may also be determined
Objective 5: Soil moisture content will be measured to a depth of 1 meter using a GPR at locations where the vertical soil moisture distribution is known. This will be accomplished by collecting spatially continuous GPR data along transects adjacent to neutron probe and TDR access tubes, and gravimetric soil sampling locations. The neutron probe method is being used because it is a considered to be the most accurate method of measuring soil moisture content in the field. TDR is being used because it is based on the same principle as the GPR. Soil samples taken adjacent to the access tubes will provide confirmation of the neutron probe and TDR data. Prior to starting the sampling events, the neutron probe and TDR will be calibrated for the soil conditions.
Objective 6. The results from this study will be presented at professional meetings and published in peer reviewed journal.
YEAR 2
Objective 1: Identify field sites for GPR testing. Sites will be selected at the University of Puerto Rico Experiment Stations at Isabela, Lajas and Fortuna. Figure 2 shows the locations of the Experiment Stations in Puerto Rico. The numbers in the figure are the Climate Divisions as defined by NOAA. Table 1 lists the soils at the three experiment Stations.
Table 1. Test site locations, soil types and Climate Zones defined by NOAA.
______
Test SiteSoil TypeClimatic Zone*
FortunaSan Antón Clay Loam (Molisols)South Coastal
IsabelaCoto Clay (Oxisol)North Coastal
LajasFraternidad Clay ______South Coastal
* see Figure 1 for Climate Zones in Puerto Rico
Objective 2: Install TDR and neutron probe access tubes. Access tubes will be installed along transects similar to those shown in Figure 1. Additionally at each sites, sprinkler irrigation systems will be installed so that the soil moisture content can be controlled.
Objective 3: Soils will be collected from the test areas for chemical and physical evaluation. Undisturbed samples will be collected from 0 to 25 cm, 25 to 50 cm, 50 to 75 cm and 75 to 100 cm. Soil samples will be analyzed as before. The physical properties will be determined as in the previous work.
Objective 4: Calibrate TDR and neutron probes. Prior to performing the GPR tests, a calibration will be conducted under field conditions on the TDR and neutron probe.
Objective 5: Conduct GPR testing. Soil moisture content will be measured to a depth of 1 meter using a GPR at locations where the vertical soil moisture distribution is known. This will be accomplished by collecting spatially continuous GPR data along transects adjacent to neutron probe and TDR access tubes, and gravimetric soil sampling locations.
Objective 6: Publish/present second year’s findings.
Budget and Schedule
The estimated budget is shown in the attached spreadsheets. Specific costs are provided for years 1 and 2 of the two year project in Table 2. The project Schedule is shown in Table 3.
Table 2b. Cost Estimate.
BUDGET JUSTIFICAITON, Field Measurements & Verification - YEAR 1Salaries and Fringe Benefits / NOAA
Eric Harmsen Academic Release Time, 8.33% (1 credit) / $3,998
Hamed Parsiani, Academic Release Time 12.5% (1.5 credit) / $7,975
Technical, Shop, and Other - Construction of Soil Pit / $1,500
One (1) Graduate Student ($9,000 per year) / $9,000
Undergraduate Students - 20hrs/wk @ $7/hr*48 wks / $6,720
Total Salaries and Wages / $31,193
Fringe Benefits, 9.2% for E5, E6, E10-E12 grades, for additional compensation / $1,424
Fringe Benefits, 1.55%, Undergraduates / $104
Total Salaries and FB / $32,721
Other Direct Costs
a. Subcontract
b. Consultant
c. Equipment and Supplies
Sprinkler Irrigation System (3 @ $300) / $900
Office supplies and copying / $200
TDR Rental / $1,600
TDR and neutron probe access tubes and installation equipment / $1,500
Neutron probe operational and safety training / $2,000
Brass Sampling Cores - 6 cm long (quantity 30) / $390
Soil Pressure Plate Extraction Kit (pressure plates, extractors, compressor, manifold) / $11,000
Refrigerator and drying oven (for soil samples) / $1,300
Analytical Balance / $650
Soil Physics and Chemistry Laboratory materials / $4,000
Field supplies / $500
Total Equipment and Supplies / $24,040
e. Travel
Local Travel / $0
Domestic Travel - 2 trips to professional meetings @ $1,500 each / $3,000
$0
Total Travel / $3,000
Total Direct Costs / $57,761
Indirect Cost / $0
Subtotal -Estimated Costs / $57,761
Table 2b.
BUDGET JUSTIFICAITON Field Measurements & Verification - YEAR 2Salaries and Fringe Benefits / NOAA
Eric Harmsen Academic Release Time, 8.33% (1 credit) / $3,998
Hamed Parsiani, Academic Release Time 12.5% (1.5 credit) / $7,975
Technical, Shop, and Other - 3 Experiment Stations @ $1,167 per Station / $3,500
One (1) Graduate Student ($9,000 per year) / $9,000
Undergraduate Students - 20hrs/wk @ $7/hr*48 wks / $6,720
Total Salaries and Wages / $31,193
Fringe Benefits, 9.2% for E5, E6, E10-E12 grades, for additional compensation / $1,424
Fringe Benefits, 1.55%, Undergraduates / $104
Total Salaries and FB / $32,721
Other Direct Costs
a. Subcontract
b. Consultant
c. Equipment and Supplies
Office supplies and copying / $200
TDR Rental / $1,600
neutron probe access tubes and installation equipment / $1,500
Neutron probe operational and safety training / $1,500
Soil Physics and Chemistry Laboratory materials / $4,000
Total Equipment and Supplies / $8,800
e. Travel
Local Travel - 15 trips at $150/trip / $2,250
Domestic Travel - 2 trips to professional meetings @ $1,500 each / $3,000
$0
Total Travel / $5,250
Publication costs / $2,000
Total Direct Costs / $48,771
Indirect Cost / $0
Subtotal -Estimated Costs / $48,771
Table 3. Project Schedule
1st Sem. 2002 / 2nd Sem. 2003 / Summer 2003 / 1st Sem. 2003 / 2nd Sem. 2004 / Summer 2004YEAR 1
1. Conduct literature review / X
2. Receive training in application of GPR method / X
3. Construct artificial soil profiles in the UPR Finca Alzamora / X
4. Analyze soils for physical and chemical characteristics / X
5. Conduct test of the GPR by comparing with traditional soil moisture measurement methods / X / X
6. Develop appropriate processing algorithms for maximum accuracy of soil moisture measurement by the GPR / X / X
7. Publish/present first years findings / X
YEAR 2
1. Identify field sites for GPR testing / X
2. Install TDR and neutron probe access tubes / X
3. Analyze soils for physical and chemical characteristics. / X / X
4. Calibrate TDR and neutron probes / X
5. Conduct GPR testing / X
6. Publish/present final results. / X
ATTACHMENT
RESULTS OF THETA PROBE CALIBRATION FOR FOUR PUERTO RICAN SOIL
The UPR Agricultural and Biosystem Engineering Department developed calibration curves for the Delta-T Theta Probe soil moisture sensor for four fine textured soils from Puerto Rico. The soils were: Fraternidad Clay, San Antón Silty Loam, Coto Clay and Daguey Clay. The Profile Probe uses a standing wave method and can be categorized alongside "capacitance" probes or "frequency-domain" probes. According to the User’s Manual: “The sensing head has an array of four rods, the outer three of which, connected to instrument ground, form an electrical shield around the central single rod. This behaves as an additional section of transmission line having an impedance that depends on dielectric constant of the matrix into which it is inserted. If this impedance differs from that of the internal transmission line, then a proportion of the signal is reflected back from the junction between the probe array and the transmission line. This reflected component interferes with the incident signal causing a voltage standing wave to be set up on the transmission line, i.e., a variation of voltage amplitude along the length of the line. ……Measuring this amplitude will give the relative impedance of the probe, hence the dielectric constant and thus a measure of the volumetric moisture content.” Detailed information on the Theta Probe is available at the following website: .
The calibration curves (Figure A1 through A4) for the four Puerto Rican fine textured soils were obtain in the following manner. The soil was allowed to air dry, after which it was sieved through a No. 200 mesh soil screen and carefully placed into a plastic container to a depth of approximately 4 inches. The lateral dimensions of the box were 10 inches by 13 inches. The Theta Probe was inserted into the surface of the soil for measuring soil moisture content. The probe was connected to a digital readout (Delta-T HH2). The Box was placed on an analytical balance having a capacity of 50 kg maximum, with an accuracy of ± 5 grams. Water was applied to the top of the soil uniformly (with spray bottle) in increments of 300 ml. Approximately 24 hours after the water was applied the Theta Probe was read and the weight of the soil and box were recorded. Water was applied every other day until the soil moisture content was sufficiently high (i.e., when water began to drain out of the holes in the bottom of the plastic box). The actual soil volume in the box was determined, after which the soil in the box was removed and dried in an oven at 105 oC for approximately three to four days. Information related to the soil volume and dry weight allowed calculation of the soil bulk density. Bulk density was needed to convert the moisture contents by weight to moisture content by volume. Figure A1 through A4 show the resulting calibration curves.
Figure A1. Coto Clay Calibration Curve.
Figure A2. Daguey Clay Calibration Curve.
Figure A3. Fraternidad Clay Calibration Curve.
Figure A4. San Anton Silty Loam Calibration Curve.