Relationship of Soil Moisture and Reflected GPS Signal Strength

Privette, Charles V.; Khalilian, Ahmad; Bridges, William B.; Katzberg, Stephen J.; Torres, Omar; Han, Young J.; Maja, Joe Mari; Qiao, Xin

doi:10.4236/ars.2016.51002

Cited by 2 publications

(2 citation statements)

References 14 publications

(18 reference statements)

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“…Hence, it is important to make sure the output difference of the two DMR channels is only due to ambient environment, rather than the circuitry noise. The two input channels inside the DMR were evaluated using a balanced RF power divider, as explained by Privette et al [16], and the signal-to-noise ratio (SNR) of each channel was recorded. In 2014, the system was also calibrated over a surface with known reflectivity, which was a circular plastic container (2.4 m diameter and 0.3 m deep) filled with water.…”

Section: System Calibration and Resolutionmentioning

confidence: 99%

Evaluating Reflected GPS Signal as a Potential Tool for Cotton Irrigation Scheduling

Qiao¹,

Khalilian²,

Payero³

et al. 2016

ARS

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Accurate soil moisture content measurements are vital to precision irrigation management. Remote sensing using the microwave spectrum (such as GPS signals) has been used for measuring large area soil moisture contents. In our previous work, we estimated surface soil moisture contents for bare soil using a GPS Delay Mapping Receiver (DMR) developed by NASA. However, the effect of vegetation was not considered in these studies. Hence the objectives of this study were to: 1) investigate the feasibility of using DMR to determine soil moisture content in cotton production fields; 2) evaluate the attenuation effect of vegetation (cotton) on reflected GPS signal. Field experiments were conducted during the 2013 and 2014 growing seasons in South Carolina. GPS antennas were mounted at three heights (1.6, 2.7, and 4.2 m) over cotton fields to measure reflected GPS signals (DMR readings). DMR readings, soil core samples, and plant measurements were collected about once a week and attenuation effect of plant canopy was calculated. Results showed that DMR was able to detect soil moisture changes within one week after precipitation events that were larger than 25 mm per day. However, the DMR readings were poorly correlated with soil volumetric water content during dry periods. Attenuation effect of plant canopy was not significant. For irrigation purpose, the results suggested that the sensitivity of reflected GPS signals to soil moisture changes needed to be further studied before this technology could be utilized for irrigation scheduling in cotton production. Refinement of this technology will expand the use of advanced remote sensing technology for site-specific and timely irrigation scheduling. This would eliminate the need to install moisture sensors in production fields, which can interfere with farming operations and increase production costs.

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Section: System Calibration and Resolutionmentioning

confidence: 99%

Evaluating Reflected GPS Signal as a Potential Tool for Cotton Irrigation Scheduling

Qiao¹,

Khalilian²,

Payero³

et al. 2016

ARS

Self Cite

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“…Both missions operate in the microwave L-band, which is most suitable for SM observations [12,20]. Moreover, first SM retrievals have been carried out by GNSS (Global Navigation Satellite System) reflectometry approaches [21][22][23][24][25][26][27], which analyse GNSS signals reflected from the soil. Depending on the moisture content in the soil, the reflected pattern changes, which is in principle quite similar to active microwave remote sensing.…”

Section: Introductionmentioning

confidence: 99%

Soil Moisture Retrieval Based on GPS Signal Strength Attenuation

Koch

Schlenz

Prasch

et al. 2016

Water

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Soil moisture (SM) is a highly relevant variable for agriculture, the emergence of floods and a key variable in the global energy and water cycle. In the last years, several satellite missions have been launched especially to derive large-scale products of the SM dynamics on the Earth. However, in situ validation data are often scarce. We developed a new method to retrieve SM of bare soil from measurements of low-cost GPS (Global Positioning System) sensors that receive the freely available GPS L1-band signals. The experimental setup of three GPS sensors was installed at a bare soil field at the German Weather Service (DWD) in Munich for almost 1.5 years. Two GPS antennas were installed within the soil column at a depth of 10 cm and one above the soil. SM was successfully retrieved based on GPS signal strength losses through the integral soil volume. The results show high agreement with measured and modelled SM validation data. Due to its non-destructive, cheap and low power setup, GPS sensor networks could also be used for potential applications in remote areas, aiming to serve as satellite validation data and to support the fields of agriculture, water supply, flood forecasting and climate change.

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Relationship of Soil Moisture and Reflected GPS Signal Strength

Cited by 2 publications

References 14 publications

Evaluating Reflected GPS Signal as a Potential Tool for Cotton Irrigation Scheduling

Evaluating Reflected GPS Signal as a Potential Tool for Cotton Irrigation Scheduling

Soil Moisture Retrieval Based on GPS Signal Strength Attenuation

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