University of Arizona Institute of Atmospheric Physics Page 1 Wide-Area Soil Moisture Estimation Using the Propagation of Low-Frequency Electromagnetic Signals William Scheftic (Graduate Student, Atmospheric Sciences, University of Arizona) Kenneth L. Cummins and E. Philip Krider (Atmospheric Sciences, University of Arizona) David Goodrich, Susan Moran, and Russell Scott (USDA Southwest Watershed Research Center)

University of Arizona Institute of Atmospheric Physics Page 2 Discussion Outline - Finite soil surface conductivity has a quantifiable effect on surface-wave radio propagation in the 100 kHz to 1 MHz range -Brief theoretical explanation - Lightning Based method -Methodology -Preliminary results -Some Limitations - Radio transmission method -Overview of summer 2007 field campaign

University of Arizona Institute of Atmospheric Physics Page 3 Freq [Hz] Signal Attenuation Phase [rad] Conductivity = 10 mS/m; Propagation distance = 100 km Effect of finite conductivity on surface-wave signal propagation (propagation model of Norton, 1937):

University of Arizona Institute of Atmospheric Physics Page 4 Variation with Conductivity Soil – Low pass filter on propagating fields Smaller conductivity or larger distance: lower cutoff- frequency

University of Arizona Institute of Atmospheric Physics Page 5 Electrical conductivity varies with soil moisture content Percent soil saturation Electrical Conductivity (mS/m) σ=2. %W=0.34

University of Arizona Institute of Atmospheric Physics Page 6 Lightning Background Cloud-to-ground lightning electromagnetic fields: (b) First, and (c) Subsequent strokes

University of Arizona Institute of Atmospheric Physics Page 7 Rise-time determined by the highest frequencies

University of Arizona Institute of Atmospheric Physics Page 8 Propagation Animation - 75->450 km distance Conductivity = 5 mS/m 75 km

University of Arizona Institute of Atmospheric Physics Page 9 75 km Propagation Animation - 75->450 km distance

University of Arizona Institute of Atmospheric Physics Page km Propagation Animation - 75->450 km distance

University of Arizona Institute of Atmospheric Physics Page km Propagation Animation - 75->450 km distance

University of Arizona Institute of Atmospheric Physics Page km Propagation Animation - 75->450 km distance

University of Arizona Institute of Atmospheric Physics Page km Propagation Animation - 75->450 km distance

University of Arizona Institute of Atmospheric Physics Page km Propagation Animation - 75->450 km distance

University of Arizona Institute of Atmospheric Physics Page 15 Rudimentary LTG Method 200 km Lordsburg Tucson Williams Window Rock Yuma Select desired path for analysis Starting at a polygon that defines the lightning- observation region Ending at a sensor location (e.g., Lordsburg; Williams) Evaluate risetime of lightning waveform measured by the selected sensor. Convert risetime to apparent electrical conductivity Convert apparent conductivity to soil moisture Used North American Regional Reanalysis (NARR) as validation Polygon Path Sensor

University of Arizona Institute of Atmospheric Physics Page 16 Average Risetime over U.S.

University of Arizona Institute of Atmospheric Physics Page 17 Distribution of Risetime And Soil Moisture

University of Arizona Institute of Atmospheric Physics Page 18 Soil Moisture vs. Conductivity (loose criteria)

University of Arizona Institute of Atmospheric Physics Page 19 Soil Moisture vs. Conductivity (weighted count > 35)

University of Arizona Institute of Atmospheric Physics Page 20 Limitations Other factors affect conductivity changes Soil temperature, soil salinity, conductivity gradient over a several-meter depth No perfect set of wide-area data for validation NARR can miss precipitation events as occurred for at least one of the 2005 lightning events. The size of the lightning region being analyzed determines how similar lightning to sensor paths really are. Must have lightning!!

University of Arizona Institute of Atmospheric Physics Page 21 An alternate signal source is man-made narrow-band radio signals (LORAN, NDB, AM radio stations) SaSa ScSc SbSb Tx dcdc dada d ab Longitude Latitude

University of Arizona Institute of Atmospheric Physics Page 22 The effect can be seen as changes in magnitude and phase for narrow-band radio signals φ μSec E

University of Arizona Institute of Atmospheric Physics Page 23 RadioTX Field Campaign ‘07 June->October Field Campaign in San Pedro Basin Three broadband sensors Remote control from PAS Measure mag/phase vs. fq. Derive conductivity Correlate with WG and San Pedro in- situ measurements, and NARR Note: 18 AM transmitter within 100km of Tombstone

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University of Arizona Institute of Atmospheric Physics Page kHz NDB

University of Arizona Institute of Atmospheric Physics Page kHz AM station

University of Arizona Institute of Atmospheric Physics Page 27 Questions ?

University of Arizona Institute of Atmospheric Physics Page 28 Supporting Material

University of Arizona Institute of Atmospheric Physics Page 29 Wide-area Validation: North American Regional Reanalysis Specifications 32 km resolution, every 3 hours Available from Jan 1979 through Feb 2007 Adequate representation of hydrologic balance Uses NOAH LSM ver soil depth layers Uses hourly rain gauge data and PRISM technique to assimilate precipitation

University of Arizona Institute of Atmospheric Physics Page 30 Soil Moisture: NARR Vs. ARS In-Situ

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