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USGS2020

Exploring the potential value of satellite remote sensing to monitor chlorophyll-a for U.S. lakes and reservoirs

Assessment of chlorophyll-a, an algal pigment, typically measured by field and laboratory in situ analyses, is used to estimate algal abundance and trophic status in lakes and reservoirs. In situ-based monitoring programs can be expensive, may not be spatially, and temporally comprehensive and results may not be available in the timeframe needed to make some management decisions, but can be more accurate, precise, and specific than remotely sensed measures. Satellite remotely sensed chlorophyll-a offers the potential for more geographically and temporally dense data collection to support estimates when used to augment or substitute for in situ measures. In this study, we compare available chlorophyll-a data from in situ and satellite imagery measures at the national scale and perform a cost analysis of these different monitoring approaches. The annual potential avoided costs associated with increasing the availability of remotely sensed chlorophyll-a values were estimated to range between $5.7 and $316 million depending upon the satellite program used and the timeframe considered. We also compared sociodemographic characteristics of the regions (both public and private lands) covered by both remote sensing and in situ data to check for any systematic differences across areas that have monitoring data. This analysis underscores the importance of continued support for both field-based in situ monitoring and satellite sensor programs that provide complementary information to water quality managers, given increased challenges associated with eutrophication, nuisance, and harmful algal bloom events.

Environmental Monitoring and Assessment↗

USGS2014

Uncertainty estimates in broadband seismometer sensitivities using microseisms

The midband sensitivity of a seismic instrument is one of the fundamental parameters used in published station metadata. Any errors in this value can compromise amplitude estimates in otherwise high-quality data. To estimate an upper bound in the uncertainty of the midband sensitivity for modern broadband instruments, we compare daily microseism (4- to 8-s period) amplitude ratios between the vertical components of colocated broadband sensors across the IRIS/USGS (network code IU) seismic network. We find that the mean of the 145,972 daily ratios used between 2002 and 2013 is 0.9895 with a standard deviation of 0.0231. This suggests that the ratio between instruments shows a small bias and considerable scatter. We also find that these ratios follow a standard normal distribution ( R 2  = 0.95442), which suggests that the midband sensitivity of an instrument has an error of no greater than ±6 % with a 99 % confidence interval. This gives an upper bound on the precision to which we know the sensitivity of a fielded instrument.

Journal of Seismology↗

USGS2022

A review of near-surface QS estimation methods using active and passive sources

Seismic attenuation and the associated quality factor ( Q ) have long been studied in various sub-disciplines of seismology, ranging from observational and engineering seismology to near-surface geophysics and soil/rock dynamics with particular emphasis on geotechnical earthquake engineering and engineering seismology. Within the broader framework of seismic site characterization, various experimental techniques have been adopted over the years to measure the near-surface shear-wave quality factor ( Q S ). Common methods include active- and passive-source recording techniques performed at the free surface of soil deposits and within boreholes, as well as laboratory tests. This paper intends to provide an in-depth review of what Q is and, in particular, how Q S is estimated in the current practice. After motivating the importance of this parameter in seismology, we proceed by recalling various theoretical definitions of Q and its measurement through laboratory tests, considering various deformation modes, most notably Q P and Q S . We next provide a review of the literature on Q S estimation methods that use data from surface and borehole sensor recordings. We distinguish between active- and passive-source approaches, along with their pros and cons, as well as the state-of-the-practice and state-of-the-art. Finally, we summarize the phenomena associated with the high-frequency shear-wave attenuation factor (kappa) and its relation to Q , as well as other lesser-known attenuation parameters.

Journal of Seismology↗

USGS2025

Applications of unoccupied aerial systems (UAS) in landscape ecology: A review of recent research, challenges and emerging opportunities

Context Unoccupied aerial systems/vehicles (UAS/UAV, a.k.a. drones) have become an increasingly popular tool for ecological research. But much of the recent research is concerned with developing mapping and detection approaches, with few studies attempting to link UAS data to ecosystem processes and function. Landscape ecologists have long used high resolution imagery and spatial analyses to address ecological questions and are therefore uniquely positioned to advance UAS research for ecological applications. Objectives The review objectives are to: (1) provide background on how UAS are used in landscape ecological studies, (2) identify major advancements and research gaps, and (3) discuss ways to better facilitate the use of UAS in landscape ecology research. Methods We conducted a systematic review based on PRISMA guidelines using key search terms that are unique to landscape ecology research. We reviewed only papers that applied UAS data to investigate questions about ecological patterns, processes, or function. Results We summarize metadata from 161 papers that fit our review criteria. We highlight and discuss major research themes and applications, sensors and data collection techniques, image processing, feature extraction and spatial analysis, image fusion and satellite scaling, and open data and software. Conclusion We observed a diversity of UAS methods, applications, and creative spatial modeling and analysis approaches. Key aspects of UAS research in landscape ecology include modeling wildlife micro-habitats, scaling of ecosystem functions, landscape and geomorphic change detection, integrating UAS with historical aerial and satellite imagery, and novel applications of spatial statistics.

Landscape Ecology↗

USGS2013

Phreatophytes under stress: transpiration and stomatal conductance of saltcedar ( Tamarix spp.) in a high-salinity environment

Background and aims: We sought to understand the environmental constraints on an arid-zone riparian phreatophtye, saltcedar (Tamarix ramosissima and related species and hybrids), growing over a brackish aquifer along the Colorado River in the western U.S. Depth to groundwater, meteorological factors, salinity and soil hydraulic properties were compared at stress and non-stressed sites that differed in salinity of the aquifer, soil properties and water use characteristics, to identify the factors depressing water use at the stress site. Methods: Saltcedar leaf-level transpiration (EL), LAI, and stomatal conductance (GS) were measured over a growing season (June–September) with Granier and stem heat balance sensors and were compared to those for saltcedar at the non-stress site determined in a previous study. Transpiration on a ground-area basis (EG) was calculated as EL × LAI. Environmental factors were regressed against hourly and daily EL and GS at each site to determine the main factors controlling water use at each site. Results: At the stress site, mean EG over the summer was only 30 % of potential evapotranspiration (ETo). GS and EG peaked between 8 and 9 am then decreased over the daylight hours. Daytime GS was negatively correlated with vapor pressure deficit (VPD) (P < 0.05). By contrast, EG at the non-stress site tracked the daily radiation curve, was positively correlated with VPD and was nearly equal to ETo on a daily basis. Depth to groundwater increased over the growing season at both sites and resulted in decreasing EG but could not explain the difference between sites. Both sites had high soil moisture levels throughout the vadose zone with high calculated unsaturated conductivity. However, salinity in the aquifer and vadose zone was three times higher at the stress site than at the non-stress site and could explain differences in plant EG and GS. Conclusions: Salts accumulated in the vadose zone at both sites so usable water was confined to the saturated capillary fringe above the aquifer. Existence of a saline aquifer imposes several types of constraints on phreatophyte EG, which need to be considered in models of plant water uptake. The heterogeneous nature of saltcedar EG over river terraces introduces potential errors into estimates of ET by wide-area methods.

Colorado River↗

USGS2024

Spaceborne imaging spectroscopy enables carbon trait estimation in cover crop and cash crop residues

Purpose Cover crops and reduced tillage are two key climate smart agricultural practices that can provide agroecosystem services including improved soil health, increased soil carbon sequestration, and reduced fertilizer needs. Crop residue carbon traits (i.e., lignin, holocellulose, non-structural carbohydrates) and nitrogen concentrations largely mediate decomposition rates and amount of plant-available nitrogen accessible to cash crops and determine soil carbon residence time. Non-destructive approaches to quantify these important traits are possible using spectroscopy. Methods The objective of this study was to quantify cash and cover crop residue nitrogen and carbon traits using partial least squares regression models and a combination of 1) the band equivalent reflectance (BER) of the PRecursore IperSpettrale della Missione Applicativa (PRISMA) imaging spectroscopy sensor derived from laboratory collected ASD spectra (n = 296) of 11 cover crop species and three cash crop species, and 2) spaceborne PRISMA imagery that coincided with destructive crop residue collections in the spring of 2022 (n = 65). Spectral range was constrained to 1200 to 2400nm to reduce the likelihood of confounding relationships in wavelengths sensitive to plant pigments or those related to canopy structure for both analytical approaches. Results Models using laboratory BER of PRISMA all demonstrated high accuracies and low errors for estimation of nitrogen and carbon traits (adj. R2 = 0.86 – 0.98; RMSE = 0.24 – 4.25%) and results suggest that a single model may be used for a given trait across all species. Models using spaceborne imaging spectroscopy demonstrated that crop residue carbon traits can be successfully estimated using PRISMA imagery (adj. R2 = 0.65 – 0.75; RMSE = 2.71 – 4.16%). We found moderate relationships between nitrogen concentration and PRISMA imagery (adj. R2 = 0.52; RMSE = 0.25%), which is partly related to the range of nitrogen in these senesced crop residues (0.38 – 1.85%). PRISMA imagery models were also impacted by atmospheric absorption, variability in surface moisture content, and some presence of green vegetation. Conclusion As spaceborne imaging spectroscopy data become more widely available from upcoming missions, crop residue trait estimates could be regularly generated and integrated into decision support tools to calculate decomposition rates and associated nitrogen credits to inform precision field management, as well as to enable measurement, monitoring, reporting, and verification of net carbon benefits from climate smart agricultural practice adoption in an emerging carbon marketplace.

Maryland↗

USGS2004

RADAR: The Cassini Titan Radar Mapper

The Cassini RADAR instrument is a multimode 13.8 GHz multiple-beam sensor that can operate as a synthetic-aperture radar (SAR) imager, altimeter, scatterometer, and radiometer. The principal objective of the RADAR is to map the surface of Titan. This will be done in the imaging, scatterometer, and radiometer modes. The RADAR altimeter data will provide information on relative elevations in selected areas. Surfaces of the Saturn’s icy satellites will be explored utilizing the RADAR radiometer and scatterometer modes. Saturn’s atmosphere and rings will be probed in the radiometer mode only. The instrument is a joint development by JPL/NASA and ASI. The RADAR design features significant autonomy and data compression capabilities. It is expected that the instrument will detect surfaces with backscatter coefficient as low as −40 dB.

Space Science Reviews↗

USGS2026

Suspended-sediment and phosphorus response in a fire-affected central Montana headwater catchment

Purpose Eutrophication and nuisance filamentous algal blooms (i.e. Cladophora ) are increasingly common occurrences throughout much of the western United States. Wildfire may be contributing to the frequency and magnitude of algal blooms through excess sediment and nutrient loading to streams and rivers. Our objective was to evaluate the effects the 2021 Woods Creek Fire had on sediment yields and phosphorus (total and bioavailable) partitioning in Camas Creek, a major tributary to the Smith River in Montana where Cladophora are now consistently reaching nuisance levels. Methods We collected water quality samples during snowmelt pulsing events as well as fixed interval sampling using an established U.S. Geological Survey stream gage instrumented with a continuous water quality sonde and an automatic peristaltic pump sampler. Water samples were processed for total phosphorus (TP), sediment-bound bioavailable phosphorus (S-BioP), soluble reactive phosphorus (SRP), and suspended sediment concentrations and were evaluated using linear regression and other nonparametric statistical tests. Continuous turbidity and streamflow were evaluated using hysteresis analysis to determine sediment sourcing and connectivity. Results We found that the Woods Creek Fire did not significantly influence TP and S-BioP in Camas Creek. However, there was a significant increase in SRP and turbidity in both postfire years (2022 and 2023). Hysteresis analysis of 91 delineated events indicated positive (clockwise) hysteresis was the dominant event pattern during the snowmelt period. This may indicate a lower hillslope to channel connectivity, with the major sediment supply originating from the channel and/or riparian areas. Conclusion Results from this study demonstrate the benefits of combining discrete water quality samples with high-frequency turbidity sensors to characterize postfire sediment and phosphorus dynamics. While a lack of postfire response in TP and S-BioP is contrary to many other studies, our findings highlight the role climate and catchment morphology play in attenuating a disturbance effect.

Montana↗

USGS2025

“Leaky weirs” capture alluvial deposition and enhance seasonal mountain-front recharge in dryland streams

“Leaky weirs” are rock structures installed in dryland streams, which are anchored into exposed bedrock, loosely cemented, and designed to allow water to slowly pass through. They are being tested at a ranch in southeastern Arizona, USA, to restore and conserve the historic range and desert wetlands. Data are collected to assess how leaky weirs impact surface water, subsurface water, and groundwater recharge—including stream discharge, timing, and depth of infiltration, and groundwater elevations. Three adjacent watersheds, two with outlets just below leaky weirs and one with leaky weirs farther upstream, were instrumented with water-level loggers, wildlife cameras, and crest stage instruments with temperature sensors in the soil. As most groundwater recharge is assumed to be focused along the mountain fronts in this region, mountain-block recharge is also evaluated to differentiate between the two using isotope analyses. Finally, a single, late-season flood event is scrutinized to consider the leaky weir effect on all monitored components in the water budget. Results indicated groundwater flow is primarily from the mountains to the east via older, regional mountain-block recharge. However, the development of shallow alluvial aquifers is supported by the leaky weirs, that slow flows, capture permeable sediments, and allow infiltration, thus enhancing mountain-front recharge. In turn, these new pockets of water help support the restoration of historic wetlands. Sediment accumulates where leaky weirs are installed, reducing flashy peak flows, and resulting in a series of infiltration ponds along the channel that support vegetation during growing seasons and recharge the shallow aquifer during non-growing seasons.

Arizona↗

USGS2019

Towards determining spatial methane distribution on Arctic permafrost bluffs with an unmanned aerial system

Arctic permafrost stores vast amounts of methane (CH 4 ) in subsurface reservoirs. Thawing permafrost creates areas for this potent greenhouse gas to be released to the atmosphere. Identifying ‘hot spots’ of methane flux on a local scale has been limited by the spatial scales of traditional ground-based or satellite-based methane-sampling methods. Here we present a reliable and an easily replicable design using only off-the-shelf, cost-effective methane sensor components and an Unmanned Aerial System (UAS). Our results demonstrate the high efficiency of the design and the advantages of this methodology for environmental methane studies that are subjected to the high spatial variability of methane levels. On Barter Island, NE Alaska, we noted spikes in CH 4 concentrations coincident with topographic features or anomalies. Such spikes may be attributed to enhanced land/air transfer and may reveal zones of high methane production and/or minimal oxidation in areas of thermoerosional gullies along thawing coastal zones. Thermoerosional gullies represent hotspots that release significantly higher levels of methane than the surrounding areas, thus suggesting that point sampling is inadequate in characterizing methane releases and that increasing rates of permafrost thaw may result in increasing point sources of high CH 4 emissions.

SN Applied Sciences↗

USGS1989

Viking landing sites, remote-sensing observations, and physical properties of Martian surface materials

Important problems that confront future scientific exploration of Mars include the physical properties of Martian surface materials and the geologic processes that formed the materials. The design of landing spacecraft, roving vehicles, and sampling devices and the selection of landing sites, vehicle traverses, and sample sites will be, in part, guided by the physical properties of the materials. Four materials occur in the sample fields of the Viking landers: (1) drift, (2) crusty to cloddy, (3) blocky, and (4) rock. The first three are soillike. Drift materials is weak, loose, and porous. We estimate that it has a dielectric constant near 2.4 and a thermal inertia near 1 × 10 −3 to 3 × 10 −3 ( cal cm −2 sec 1 2 K −1 ) "> 1 × 10 −3 to 3 × 10 −3 (cal cm −2 sec 12 K −1 ) because of its low bulk density, fine grain size, and small cohesion. Crusty to cloddy material is expected to have a dielectric constant near 2.8 and a thermal inertia near 4 × 10 −3 to 7 × 10 −3 because of its moderate bulk density and cementation of grains. Blocky material should have a dielectric constant near 3.3 and a thermal inertia near 7 × 10 −3 to 9 × 10 −3 because of its moderate bulk density and cementation. Common basaltic rocks have dielectric constants near 8 and thermal inertias near 30 × 10 −3 to 60 × 10 −3 . Comparisons of estimated dielectric constants and thermal inertias of the materials at the landing sites with those obtained remotely by Earth-based radars and Viking Orbiter thermal sensors suggest that the materials at the landing sites are good analogs for materials elsewhere on Mars. Correlation of remotely estimated dielectric constant and thermal inertias indicates two modal values for paired values of dielectric constants and thermal inertias near (A) 2 and 2 × 10 −3 and (B) 3 and 6 × 10 −3 , respectively. These two modes are comparable to the dielectric constants and thermal inertias for drift and crusty to cloddy material, respectively. Dielectric constants and thermal inertias for blocky material are larger but consistent with values in the northern plains. Our interpretations are compatible with an aeolian origin for drift and similar materials elsewhere on Mars. The postulate that moderate dielectric constants and thermal inertias larger than 3 or 4 × 10 −3 are produced by cementation of soillike materials is partly consistent with the data. The average dielectric constant and thermal inertia and their correlation with one another suggest that most of the surface of Mars should present few difficulties to future surface exploration, but some surfaces may present difficulties for spacecraft that are not suitably designed.

Icarus↗

USGS1983

A system for measuring bottom profile, waves and currents in the high-energy nearshore environment

A new data-acquisition system capable of measuring waves, currents and the nearshore profile in breaking waves as high as 5 m has been developed and successfully field-tested. Components of the mechanical system are a sled carrying a vertical mast, a double-drum winch placed landward of the beach, and a line that runs from one drum of the winch around three blocks, which are the corners of a right triangle, to the other drum of the winch. The sled is attached to the shore-normal side of the triangular line arrangement and is pulled offshore by one drum of the winch and onshore by the other. The profile is measured as the sled is towed along the shore-normal transect using an infrared rangefinder mounted landward of the winch and optical prisms mounted on top of the sled's mast. A pressure sensor and two-axis electromagnetic current meter are mounted on the frame of the sled. These data are encoded on the sled and telemetered to a receiving/recording station onshore. Preliminary results suggest that near-bottom offshore-flowing currents during periods of high-energy swell are important in forcing changes to the configuration of the nearshore profile.

Marine Geology↗

USGS1990

Spectral estimates of net radiation and soil heat flux

Conventional methods of measuring surface energy balance are point measurements and represent only a small area. Remote sensing offers a potential means of measuring outgoing fluxes over large areas at the spatial resolution of the sensor. The objective of this study was to estimate net radiation (R n ) and soil heat flux (G) using remotely sensed multispectral data acquired from an aircraft over large agricultural fields. Ground-based instruments measured R n and G at nine locations along the flight lines. Incoming fluxes were also measured by ground-based instruments. Outgoing fluxes were estimated using remotely sensed data. Remote R n , estimated as the algebraic sum of incoming and outgoing fluxes, slightly underestimated R n measured by the ground-based net radiometers. The mean absolute errors for remote R n minus measured R n were less than 7%. Remote G, estimated as a function of a spectral vegetation index and remote R n , slightly overestimated measured G; however, the mean absolute error for remote G was 13%. Some of the differences between measured and remote values of R n and G are associated with differences in instrument designs and measurement techniques. The root mean square error for available energy (R n - G) was 12%. Thus, methods using both ground-based and remotely sensed data can provide reliable estimates of the available energy which can be partitioned into sensible and latent heat under nonadvective conditions.

Remote Sensing of Environment↗

USGS1993

The role of acoustic emission in the study of rock fracture

The development of faults and shear fracture systems over a broad range of temperature and pressure and for a variety of rock types involves the growth and interaction of microcracks. Acoustic emission (AE), which is produced by rapid microcrack growth, is a ubiquitous phenomenon associated with brittle fracture and has provided a wealth of information regarding the failure process in rock. This paper reviews the successes and limitations of AE studies as applied to the fracture process in rock with emphasis on our ability to predict rock failure. Application of laboratory AE studies to larger scale problems related to the understanding of earthquake processes is also discussed. In this context, laboratory studies can be divided into the following categories. 1) Simple counting of the number of AE events prior to sample failure shows a correlation between AE rate and inelastic strain rate. Additional sorting of events by amplitude has shown that AE events obey the power law frequency-magnitude relation observed for earthquakes. These cumulative event count techniques are being used in conjunction with damage mechanics models to determine how damage accumulates during loading and to predict failure. 2) A second area of research involves the location of hypocenters of AE source events. This technique requires precise arrival time data of AE signals recorded over an array of sensors that are essentially a miniature seismic net. Analysis of the spatial and temporal variation of event hypocenters has improved our understanding of the progression of microcrack growth and clustering leading to rock failure. Recently, fracture nucleation and growth have been studied under conditions of quasi-static fault propagation by controlling stress to maintain constant AE rate. 3) A third area of study involves the analysis of full waveform data as recorded at receiver sites. One aspect of this research has been to determine fault plane solutions of AE source events from first motion data. These studies show that in addition to pure tensile and double couple events, a significant number of more complex event types occur in the period leading to fault nucleation. 4) P and S wave velocities (including spatial variations) and attenuation have been obtained by artificially generating acoustic pulses which are modified during passage through the sample. ?? 1993.

International Journal of Rock Mechanics and Mining↗

USGS1987

Calculation of solar radiation in mountainous terrain

A study was performed to assess the accuracy of a daily solar radiation model for horizontal or sloping sites in terrain where surrounding ridges and tall trees block both direct beam and diffuse sky short wave radiation. To simulate adequately the major effects of these environments on radiation, the model incorporated (1) standard treatment of solar geometry (after Harris, 1983); (2) separation of direct and diffuse radiation by considering scattering and absorption due to aerosols, water vapor, air molecules and ozone (after Iqbal, 1983); (3) anisotropy of diffuse radiation modeled as a circumsolar component (15–50% of the total clear sky diffuse) plus an isotropic background; and (4) proper calculation of the proportions of sky radiation and ground reflected radiation sensed by both horizontal and inclined sensors. The model was calibrated using data from both horizontal and inclined pyranometers at six sites over four years. Values for the Ångstrom turbidity coefficient and the percentage of circumsolar diffuse radiation were determined using an iterative best fit technique. Mean monthly values of these coefficients and mean monthly ozone and water vapor concentrations from nearby weather service stations could be used for predicting total, cloud free, daily radiation with acceptable accuracy. Required site measurements include slope, aspect, latitude, longitude, date, time, effective horizon for the site, and an assessment of albedo for the surrounding terrain (including vegetation).

Agricultural and Forest Meteorology↗

USGS1990

Sediment movement along the U.S. east coast continental shelf-I. Estimates of bottom stress using the Grant-Madsen model and near-bottom wave and current measurements

Bottom stress is calculated for several long-term time-series observations, made on the U.S. east coast continental shelf during winter, using the wave-current interaction and moveable bed models of Grant and Madsen (1979, Journal of Geophysical Research, 84, 1797-1808; 1982, Journal of Geophysical Research, 87, 469-482). The wave and current measurements were obtained by means of a bottom tripod system which measured current using a Savonius rotor and vane and waves by means of a pressure sensor. The variables were burst sampled about 10% of the time. Wave energy was reasonably resolved, although aliased by wave groupiness, and wave period was accurate to 1-2 s during large storms. Errors in current speed and direction depend on the speed of the mean current relative to the wave current. In general, errors in bottom stress caused by uncertainties in measured current speed and wave characteristics were 10-20%. During storms, the bottom stress calculated using the Grant-Madsen models exceeded stress computed from conventional drag laws by a factor of about 1.5 on average and 3 or more during storm peaks. Thus, even in water as deep as 80 m, oscillatory near-bottom currents associated with surface gravity waves of period 12 s or longer will contribute substantially to bottom stress. Given that the Grant-Madsen model is correct, parameterizations of bottom stress that do not incorporate wave effects will substantially underestimate stress and sediment transport in this region of the continental shelf.

Georges Bank, Mid-Atlantic Bight↗

USGS2015

On the prediction of threshold friction velocity of wind erosion using soil reflectance spectroscopy

Current approaches to estimate threshold friction velocity (TFV) of soil particle movement, including both experimental and empirical methods, suffer from various disadvantages, and they are particularly not effective to estimate TFVs at regional to global scales. Reflectance spectroscopy has been widely used to obtain TFV-related soil properties (e.g., moisture, texture, crust, etc.), however, no studies have attempted to directly relate soil TFV to their spectral reflectance. The objective of this study was to investigate the relationship between soil TFV and soil reflectance in the visible and near infrared (VIS–NIR, 350–2500 nm) spectral region, and to identify the best range of wavelengths or combinations of wavelengths to predict TFV. Threshold friction velocity of 31 soils, along with their reflectance spectra and texture were measured in the Mojave Desert, California and Moab, Utah. A correlation analysis between TFV and soil reflectance identified a number of isolated, narrow spectral domains that largely fell into two spectral regions, the VIS area (400–700 nm) and the short-wavelength infrared (SWIR) area (1100–2500 nm). A partial least squares regression analysis (PLSR) confirmed the significant bands that were identified by correlation analysis. The PLSR further identified the strong relationship between the first-difference transformation and TFV at several narrow regions around 1400, 1900, and 2200 nm. The use of PLSR allowed us to identify a total of 17 key wavelengths in the investigated spectrum range, which may be used as the optimal spectral settings for estimating TFV in the laboratory and field, or mapping of TFV using airborne/satellite sensors.

Aeolian Research↗

USGS2017

A method for quantifying cloud immersion in a tropical mountain forest using time-lapse photography

Quantifying the frequency, duration, and elevation range of fog or cloud immersion is essential to estimate cloud water deposition in water budgets and to understand the ecohydrology of cloud forests. The goal of this study was to develop a low-cost and high spatial-coverage method to detect occurrence of cloud immersion within a mountain cloud forest by using time-lapse photography. Trail cameras and temperature/relative humidity sensors were deployed at five sites covering the elevation range from the assumed lifting condensation level to the mountain peaks in the Luquillo Mountains of Puerto Rico. Cloud-sensitive image characteristics (contrast, the coefficient of variation and the entropy of pixel luminance, and image colorfulness) were used with a k -means clustering approach to accurately detect cloud-immersed conditions in a time series of images from March 2014 to May 2016. Images provided hydrologically meaningful cloud-immersion information while temperature-relative humidity data were used to refine the image analysis using dew point information and provided temperature gradients along the elevation transect. Validation of the image processing method with human-judgment based classification generally indicated greater than 90% accuracy. Cloud-immersion frequency averaged 80% at sites above 900 m during nighttime hours and 49% during daytime hours, and was consistent with diurnal patterns of cloud immersion measured in a previous study. Results for the 617 m site demonstrated that cloud immersion in the Luquillo Mountains rarely occurs at the previously-reported cloud base elevation of about 600 m (11% during nighttime hours and 5% during daytime hours). The framework presented in this paper will be used to monitor at a low cost and high spatial resolution the long-term variability of cloud-immersion patterns in the Luquillo Mountains, and can be applied to ecohydrology research at other cloud-forest sites or in coastal ecosystems with advective sea fog.

El Yunque National Forest, Puerto Rico↗