Date of Graduation

8-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Civil Engineering

Advisor/Mentor

Coffman, Richard A.

Committee Member

Bernhardt-Barry, Michelle L.

Second Committee Member

Tullis, Jason A.

Third Committee Member

Oommen, Thomas

Keywords

Soil Observation Laser Absorption Spectrometer; SOLAS; Soil surfaces; Soil properties

Abstract

The hydromechanical behavior of soil is governed by parameters that include the moisture content, soil matric potential, texture, and the mineralogical composition of the soil. Remote characterization of these and other key properties of the soil offers advantages over conventional in situ or laboratory-based measurements: information may be acquired rapidly over large, or inaccessible areas; samples do not need to be collected; and the measurements are non-destructive. A field-deployable, ground-based remote sensor, designated the Soil Observation Laser Absorption Spectrometer (SOLAS), was developed to infer parameters of bare soils and other natural surfaces over intermediate (100 m) and long (1,000 m) ranges.

The SOLAS methodology combines hyperspectral remote sensing with differential absorption and laser ranging measurements. A transmitter propagates coherent, near-infrared light at on-line (823.20 nm) and off-line (847.00 nm) wavelengths. Backscattered light is received through a 203-mm diameter telescope aperture and is divided into two channels to enable simultaneous measurements of spectral reflectance, differential absorption, and range to the target. The spectral reflectance is measured on 2151 continuous bands that range from visible (380 nm) to shortwave infrared (2500 nm) wavelengths. A pair of photodetectors receive the laser backscatter in the 820–850 nm range. Atmospheric water vapor is inferred using a differential absorption technique in conjunction with an avalanche photodetector, while range to the target is based on a frequency-modulated, self-chirped, homodyne detection scheme.

The design, fabrication, and testing of the SOLAS is described herein. The receiver was optimized for the desired backscatter measurements and assessed through a series of trials that were conducted in both indoor and outdoor settings. Spectral reflectance measurements collected at proximal range compared well with measurements collected at intermediate ranges, demonstrating the utility of the receiver. Additionally, the noise characteristics of the spectral measurements were determined across the full range of the detected wavelengths. Continued development of the SOLAS instrument will enable range-resolved and water vapor-corrected reflectance measurements over longer ranges. Anticipated applications for the SOLAS technology include rapid monitoring of earth construction projects, geohazard assessment, or ground-thruthing for current and future satellite-based multi- and hyperspectral data.

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