Rae Melloh - Academia.edu (original) (raw)

Papers by Rae Melloh

Global Biogeochemical Cycles, Jun 1, 1996

Methane (CH4) dynamics in pore water, snow pore air, and surface emissions were investigated in a... more Methane (CH4) dynamics in pore water, snow pore air, and surface emissions were investigated in a temperate poor fen in New Hampshire over several winters. Total snowfall and average air temperatures during winter months (defined as December, January, and February) were climatologic indicators of significant flux rates from this midlatitude poor fen. Average winter emissions, for the five winters ending in 1994-1995, were 20, 39, 53, 56, and 26 mg m-2 d-1, amounting to 2.0, 5.2, 6.6, 9.2, and 2.0% of the total annual fluxes, respectively. Totaling emissions over 5 years that represent low to average snowfall, winter accounted for 4.3% of emissions to the atmosphere. Winter flux rates were near 55 mg m-2 d-1 for years with average snowfall, and 25 mg m-2 d-1 for years with low snowfall. Concentrations of CH 4 sampled in pore water immediately beneath the ice were highly variable (0 to 1.1 mM). The concentration magnitude and standard deviation increased toward the fen center and correlated with spatial variation in hydrology, peat texture, and peat depth. CH 4 stores increased in the near-surface pore water as the ice cover formed. Seasonal CH 4 buildup in deeper peat began near the end of the growing season, probably due to changing transport mechanisms and temperature effects on solubility. Stored CH 4 in the 25-to 75-cm peat layer decreased by 2.7 g m-2 between January and

AGU Fall Meeting Abstracts, Dec 1, 2003

With the exception of cloud cover, the largest obstacle to producing a global daily snow cover pr... more With the exception of cloud cover, the largest obstacle to producing a global daily snow cover product using remotely sensed data is the presence of the forests, which cover much of the seasonally snow-covered portion of the world. The presence of the forest canopy influences the radiance received by the sensor in such a way that the proportion of viewable snow within a pixel changes as a function of forest properties, topography and viewing position. To explore the potential effects of sun angle and viewing geometry of satellite systems such as NOAA AVHRR and MODIS on snow cover estimation, a program has been written to estimate viewable gap fractions (VGF) across landscapes based on the Li-Strahler geometric-optical (GO) bidirectional reflectance distribution function (BRDF) model. It computes a VGF map for a specified illumination and viewing geometry using maps of forest cover and species and terrain images of slope and aspect. This study explores the effect of illumination and viewing geometry and forest properties on the VGF for the Fool's Creek Intensive Study Area (ISA) in Fraser Experimental Forest, Colorado. Intensive field measurements of the required parameters for the GO model and maps of forest properties are used to generate maps of viewable gap fractions. Hemispherical photos are used to validate model results. The results improve our understanding of the way forest canopies influence the estimation of snow cover using remotely sensed data.

Proceedings of SPIE, Jun 10, 2005

Soil moisture is highly variable in space and time and affects the performance of electromagnetic... more Soil moisture is highly variable in space and time and affects the performance of electromagnetic sensors through its effects on thermal and dielectric properties. This research focused on characterizing soil moisture variability at spatial scales relevant to the sensing of small targets. Surface moistures of the top 6 cm of soil were collected on regular grids with an impedance probe. Measurements were made at 0.1-m resolution over 3- × 4-m and 3- × 5-m grids at a short grass site on silt loam. Tall grass and bare soil sites on gravelly silt loam were sampled at 1.0-m resolution over 20- × 30-m and 10- × 30-m grids. Exponential models fit to sample variograms of the 0.1-m resolution data show that soil moistures were spatially dependent over a distance of 0.5 m. Maximum variances (variogram sill), for data collected over a four-day span following a rainfall event, increased linearly with decreased mean moisture level as the soil dried. The revealed structures can be exploited to simulate soil moisture variation temporally and spatially. The impedance probe’s ability to reproduce variation in volumetric water content observed with conventional oven drying methods was demonstrated prior to the field experiment. Separate tests demonstrated that the probes can be used interchangeably. The impact of sparse surface grass on the moisture variation measured with the probe was also demonstrated to be small under the conditions tested.

Cold Regions Science and Technology, Apr 1, 2008

High-resolution ground vehicle mobility models are used by the U.S. Army to investigate new vehic... more High-resolution ground vehicle mobility models are used by the U.S. Army to investigate new vehicle concepts, conduct force-onforce simulations, and-in the future-support terrain analysis for battle planning. Use of these models in winter conditions requires a method to realistically represent the distribution of snow depth and density over a landscape. The objective of this work was to develop a method to use a recently identified pinched-cone-shaped solution domain to map snow properties. The method was developed with stringent computational and data storage efficiency requirements in mind and is demonstrated by mapping snow depth on the Ethan Allen Firing Range in northern Vermont, USA. The pinched-cone-shaped plots in a cylindrical coordinate system r = F(θ,z) where the no-slope snow depth is taken as the vertex (0,0), the radii (r) represent the snow depth relative to the no-slope case, and r is a function of azimuth (θ) and terrain slope (z). The pinched-cone equation uses a circular function with one or two coefficients that describe the slope-azimuth-dependent expansion of the pinched cone as snow depth differentiation increases with increased terrain slope. Equations that relate the expansion coefficients and no-slope snow depth to elevation then permit continuous mapping of snow depth with respect to terrain slope, azimuth, and elevation. The mapping is applied within five forest categories (open, sparse, deciduous, mixed, and conifer). The influence of snow depth and terrain slope on vehicle speed predictions is illustrated.

Journal of Hydrometeorology, Oct 1, 2008

Forest canopies influence the proportion of the land surface that is visible from above, or the v... more Forest canopies influence the proportion of the land surface that is visible from above, or the viewable gap fraction (VGF). The VGF limits the amount of information available in satellite data about the land surface, such as snow cover in forests. Efforts to recover fractional snow cover from the spectral mixture analysis model Moderate Resolution Imaging Spectroradiometer (MODIS) snow-covered area and grain size (MODSCAG) indicate the importance of view angle effects in forested landscapes. The VGF can be estimated using both hemispherical photos and forest canopy models. For a set of stands in the Cold Land Field Processes Experiment (CLPX) sites in the Fraser Experimental Forest in Colorado, the convergence of both measurements and models of the VGF as a function of view angle supports the idea that VGF can be characterized as a function of forest properties. A simple geometric optical (GO) model that includes only between-crown gaps can capture the basic shape of the VGF as a function of view zenith angle. However, the GO model tends to underestimate the VGF compared with estimates derived from hemispherical photos, particularly at high view angles. The use of a more complicated geometric opticalradiative transfer (GORT) model generally improves estimates of the VGF by taking into account withincrown gaps. Small footprint airborne lidar data are useful for mapping forest cover and height, which makes the parameterization of the GORT model possible over a landscape. Better knowledge of the angular distribution of gaps in forest canopies holds promise for improving remote sensing of snow cover fraction.

Hydrological Processes, Dec 30, 2000

Net solar radiation often dominates the snow surface energy exchange during ablation in many coni... more Net solar radiation often dominates the snow surface energy exchange during ablation in many conifer forests. Reflection of solar radiation from the snow surface depends not only on snow properties, but also on forest litter lying on and within the snowpack. We know of no validated model reported in the literature that accounts for the influence of forest litter on snow surface energy exchanges. The purpose of this work is to test an existing algorithm's ability to accumulate forest litter in snow layers and to predict the subsequent effect of litter on the snow surface albedo. Field studies in a conifer stand of red spruce-balsam fir in northern Vermont, USA, provided key data for validation, including subcanopy radiation, meteorology, snow depth, and images of litter accumulation. We ran the litter algorithm coupled with the snow model SNTHERM for the ablation season, and predictions compared well with measurements of snow depth, snow surface litter coverage, and snow surface albedo beneath the conifer canopy. Model results suggest that for this forest and ablation season, the current litter algorithm realistically distributes litter in the snowpack through time with validated effects on snow surface litter concentration and albedo. The poor relationship between daily total wind speed and change in litter coverage on the snow surface suggest that, for this forest and ablation season, incorporating wind events into the algorithm will not improve the results.

AGU Fall Meeting Abstracts, Dec 1, 2002

The 3-dimensional organization of canopy elements impacts the retrieval of snow and soil properti... more The 3-dimensional organization of canopy elements impacts the retrieval of snow and soil properties from remote sensing platforms, and influences the optical and infrared radiative environment within the forest. The number and size of gaps within and between tree crowns determines the type and amount of information that can be obtained remotely. One of the objectives of the NASA-Cold Land

39th Aerospace Sciences Meeting and Exhibit, Jan 8, 2001

Clustering of cloud microphysical conditions, such as liquid water content (LWC) and drop size, c... more Clustering of cloud microphysical conditions, such as liquid water content (LWC) and drop size, can affect the rate and shape of ice accretion and the airworthiness of aircraft. Clustering may also degrade the accuracy of cloud LWC measurements from radars and microwave radiometers being developed by the government for remotely mapping icing conditions ahead of aircraft in flight. This paper evaluates spatial clustering of LWC in icing clouds using measurements collected during NASA research flights in the Great Lakes region. We used graphical and analytical approaches to describe clustering. The analytical approach involves determining the "average size" of clusters and computing a clustering intensity parameter. We analyzed flight data composed of 1-s-frequency LWC measurements for 12 periods ranging from 17.4 minutes (73 km) to 45.3 minutes (190 km) in duration. Graphically some flight segments showed evidence of consistency with regard to clustering patterns. Cluster intensity varied from 0.06, indicating little clustering, to a high of 2.42. Cluster lengths ranged from 0.1 minutes (0.6 km) to 4.1 minutes (17.3 km). Additional analyses will allow us to determine if clustering climatologies can be developed to characterize cluster conditions by region, time period, or weather condition.

Despite the deicing capabilities of modern aircraft, crashes still occur in icing because enginee... more Despite the deicing capabilities of modern aircraft, crashes still occur in icing because engineers cannot test for all possible conditions. Also, forecasts are still not sufficiently accurate to allow aircraft to always avoid icing. As a result, a government team is developing radar and microwave radiometer technologies for remotely mapping hazardous icing conditions ahead of aircraft (Ryerson et al., 2001). Establishing the capabilities of such systems requires consideration of the spatial properties of the cloud microphysical environment they must measure. Also, spatial fluctuation of cold, supercooled cloud microphysics affects the type and location of ice formation on airfoils, thereby strongly affecting aircraft performance. This paper describes methods we use to characterize spatial patterns of cloud liquid water content (LWC) in supercooled clouds. Analyses were performed on data collected by the NASA Glenn Research Center.

The authors thank Charles Collins and Anthony Zenk of CRREL-Alaska for their assistance in collec... more The authors thank Charles Collins and Anthony Zenk of CRREL-Alaska for their assistance in collection of ground truth data; Dr. Matthew Sturm of CRREL-Alaska for assistance with snow pit data; Dr. Steven Arcone and Allan Delaney for acquiring the impulse radar trace; and Bruce Heydlauff of the Naval Weapons Center, China Lake, California, whose expertise with the KRMS instruments and data reduction equipment was essential to the success of the mission. They also thank Dr. Alan Lohanick and Walter Tucker for their technical review of this manuscript and Dr. Anthony Gow for his review of Appendix B.

Journal of Terramechanics, Aug 1, 2009

Realistic simulation of on-and off-road vehicle performance in all weather conditions is needed b... more Realistic simulation of on-and off-road vehicle performance in all weather conditions is needed by the U.S. Army for virtual training of personnel on existing vehicles, and for new vehicle design. The virtual test site is a computer simulation representing an actual terrain defined as having spatially distributed terramechanics properties and terrain interaction with vehicles. We developed a virtual test site for Ethan Allen Firing Range (EAFR) in northern Vermont. The virtual test site for EAFR is composed of terramechanics properties including spatially distributed snow depth and density, soil type, drainage class, slope, and vegetation type. Snow depth and density were spatially distributed with regard to elevation, slope, and aspect using a surface energy balance approach. This paper evaluates whether the terramechanics representation of a virtual test site is improved by adding spatially distributed snow and soil properties, rather than using uniform properties. The evaluation was accomplished by conducting a crosscountry vehicle performance analysis using the North Atlantic Treaty Organization (NATO) Reference Mobility Model (NRMM) to validate the new algorithms for realistic spatial distribution of snow properties. The results showed that the percentage of No-Go areas for uniform snow is lower than the distributed snow by 4% for the CIV (CRREL Instrumented Vehicle), 8% for the HMMWV (High Mobility Multipurpose Wheeled Vehicle), and 5% for the Stryker vehicle. For both light vehicles, approximately 12% of the No-Go areas are classified as such because of slopes P29%. These results imply that spatial distribution of snow properties provides realistic vehicle response as opposed to having the snow properties distributed uniformly throughout the entire terrain. This represents an improvement over previous versions of the terramechanics properties.

: The timing and magnitude of winter low flows vary regionally in response to basin climate and g... more : The timing and magnitude of winter low flows vary regionally in response to basin climate and geology. This report investigates the regionalization of low flows in the White Mountain and Upland physiographic sections of New Hampshire to establish a data set that will be used in improved analytical methods for estimating winter flows. For summer and winter low flow periods, 3-, 7-, 14-and 30-day duration low flow events are estimated for various sizes of drainage areas (50 to 230 sq. mi). The likelihood of a low-flow event increases as winter proceeds in the Winter Mountains, but is more evenly distributed throughout the winter in the Upland. White Mountain streams have higher runoff volumes through all seasons, except winter. The average magnitudes of winter low-flow events in both physiographic sections are highly correlated with drainage area size. Mean basin elevation was of little additional help in explaining winter low-flow events within either physiographic section, though ...

Proceedings of Spie the International Society For Optical Engineering, 2006

$Research paper thumbnail of The effect of viewing geometry and topography on viewable gap fractions through forest canopies$

Hydrological Processes, Dec 30, 2004

The fraction of the surface under forest canopies that is visible from above, or the viewable gap... more The fraction of the surface under forest canopies that is visible from above, or the viewable gap fraction (VGF), influences a number of significant physical processes, such as the longwave radiation budget of the surface and the magnitude of diffuse irradiance. In addition, it has significant implications for the remote sensing of the surface. The VGF is dependent on canopy

Proceedings of Spie the International Society For Optical Engineering, May 1, 2006

ABSTRACT Soil moisture affects soil thermal and dielectric properties and may cause false alarms ... more ABSTRACT Soil moisture affects soil thermal and dielectric properties and may cause false alarms in detecting manmade objects when dielectric or thermal discontinuities exist in the soil. The spatial variability of soil moisture changes with time and it is important to understand this behavior because it is relevant for detection of small targets, and for modeling background moisture and temperature. Surface moisture of the top 6 cm of soil was sampled on regular grids with an impedance probe at a 0.1-m interval during wetting and drying events, both four days in duration. Maximum variances for data collected in August 2004 increased with decreasing mean moisture, as soil dried following a soaking rainfall. Maximum variances in June 2005 decreased over several days of intermittent rain as the soil rewetted following a prolonged drought. Spatially dependent ranges of approximately 0.5-m lag distance and exponential model fits were consistent among all the data sets, despite changes in moisture, moisture trend, and sample variance. The procession of spatial variation is described by variograms that transition from high to low maximum variances (sills) for wetting events, and from low to high maximum variances for drying events. A linear relationship between the maximum variance and mean of square root of ε was consistent for both years, except when the soil was incompletely wetted after a drought. The highest spatial variance in moisture that produced the most variable background for small target detection occurred as a consequence of the incomplete or uneven wetting following a drought.

Hydrological Processes, Apr 1, 2004

... PhD dissertation, Departments of Geography and Mechanical Engineering, University of Californ... more ... PhD dissertation, Departments of Geography and Mechanical Engineering, University of California at Santa Barbara. Marshall SE, Warren SG. 1987. ... 166. International Association of Hydrological Sciences: Wallingford, UK; 4350. Melloh RA, Hardy JP, Davis RE, Robinson PB. ...

Two approaches for segmenting the landscape of the Hubbard Brook Experimental Forest in north cen... more Two approaches for segmenting the landscape of the Hubbard Brook Experimental Forest in north central New Hampshire, USA (43º56 N, 71.45ºW) into snowpack energy classes for use with snow-soil models are presented. The purpose of the effort was to develop an efficient segmentation scheme, one that would require fewer model runs. Scheme 1 combined slope-aspect classes and required 540 classes to account for forest cover, solar exposure, and elevation. Scheme 2 combined slope factors and forest solar transmittances, reducing the number of required classes to 52. A discussion is included that describes how an optimal segmentation approach depends on the attributes of the drainage basin, snow model, meteorological data, and computing resources, as well as the application or research purpose.