Contributions of imaging spectroscopy to improve estimates of evapotranspiration

Abstract

Abstract:Improved estimates of evapotranspiration (ET) are needed for water resource management and irrigation scheduling. We review the use of imaging spectroscopy to capture estimates of water vapour flux and biophysical components of ET. Remote sensing has long attempted to quantify and predict ET, with most applications relying only on green vegetation indexes from multispectral imagers combined with thermal radiance and weather data. In contrast, imaging spectrometry is an advanced remote sensing technology that measures hundreds of spectral bands in the solar spectrum. Plant pigments, water, and dry matter have unique spectral signatures that can advance estimates of ET and detection of drought stress. This allows analyses based on the physics of spectroscopy and avoids a requirement for continual empirical calibration. These spectral components provide unprecedented information about plant physiological processes, which improve understanding of the regulation of water fluxes and the energy budget. Laboratory, field, and airborne studies of spectral properties in the near-and shortwave-infrared region show strong relationships with plant water relations like water content, relative water content, and water potential. Because water absorption features are spectrally independent of pigment absorptions in the visible region, they provide a new source of information about environmental conditions. These new observations from imaging spectroscopy will lead to better understanding of ecological and hydrological processes.

Linear Multi-Task Learning for Predicting Soil Properties Using Field Spectroscopy

“…The first region, ranging from 410 to 650 nm, is mostly related to the Fe oxides [19,25], with the 560 nm waveband related to OM [24,65]. The second region ranges from 850 to 1075 nm; of this, the 850-930 nm range is related to hydroxyl in Fe oxides [19,25], the 970 nm waveband is related to the soil water absorption waveband [66], the 1010 nm waveband is a hydrate-related absorption feature [67], and the 1025-1075 nm range is mostly related to the electronic transition bands of Fe 2+ or Fe 3+ [19]. The third region, ranging from 1530 to 1770 nm, is almost entirely related to soil organics [19,25].…”

Infrared thermography: A non-invasive window into thermal physiology

“…Infrared thermography (IRT) emerged as a technology in the 1960s developed by the United States military initially for nighttime surveillance and heat signature detection (Rogalski, 2012). With expansion of access to non-military, scientists, and civilians, it is now used extensively in numerous fields, including law enforcement, engineering, building assessment, medical imaging, as well as in biological (Berz and Sauer, 2007;Kouba, 2005;McCafferty, 2007) and ecological applications (Boonstra et al, 1994;Rodriguez et al, 2011). More recent advances in thermal imaging have capitalized on the sensitivity of this technique for assessing relative miniscule changes in temperature that underlie changes in peripheral blood flow, which has led to repeated suggestions that thermal imaging would be a viable diagnostic tool in veterinary and human medicine (Jones, 1998;Turner, 2001), sports medicine (Al-Nakhli et al, 2012;Hildebrandt et al, 2010), and breast cancer detection (Kerr, 2004), to name a few.…”

Random Forest Algorithm Improves Detection of Physiological Activity Embedded within Reflectance Spectra Using Stomatal Conductance as a Test Case

“…For example, the Normalized Differential Water Index (NDWI) is sensitive to water content at leaf level and only partially correlates to the same status when acquired at a distance from the plant due to severe dependency on leaf area index and crop geometry [13]. Hyperspectral reflectance spectroscopy expands the multispectral analysis, as it acquires hundreds of bands at a higher spectral resolution in a single acquisition and may better capture the physiological attenuations embedded within the spectrum [14].…”