Michael F. Jasinski

Bidirectional measurements of surface reflectance for view angle corrections of oblique imagery

Abstract An apparatus for acquiring bidirectional reflectance-factor data was constructed and used over four surface types. Data sets were obtained over a headed wheat canopy, bare soil having several different roughness conditions, playa (dry lake bed), and gypsum sand. Results are presented in terms of relative bidirectional reflectance factors (BRFs) as a function of view angle at a number of solar zenith angles, nadir BRFs as a function of solar zenith angles, and, for wheat, vegetation indices as related to view and solar zenith angles. The wheat canopy exhibited the largest BRF changes with view angle. BRFs for the red and the near-infrared (NIR) bands measured over wheat did not have the same relationship with view angle. NIR/Red ratios calculated from nadir BRFs changed by nearly a factor of 2 when the solar zenith angle changed from 20° to 50°. BRF versus view angle relationships were similar for soils having smooth and intermediate rough surfaces but were considerably different for the roughest surface. Nadir BRF versus solar-zenith angle relationships were distinctly different for the three soil roughness levels. Of the various surfaces, BRFs for gypsum sand changed the least with view angle (10% at 30°).

Estimation of subpixel vegetation density of natural regions using satellite multispectral imagery

A procedure is presented for estimating the subpixel fractional canopy density of natural or undisturbed semivegetated regions on a pixel-by-pixel basis using one satellite multispectral image and a physical modeling approach. The method involves applying a model of the bulk, nondimensional plant geometry combined with a simple model of canopy reflectance and transmittance to the red and near-infrared reflectance space of the atmospherically corrected satellite image. Shadow effects are parameterized assuming Poisson-distributed and geometrically similar plant canopies. The method is applied to the estimation of fractional cover and leaf area index, using Landsat thematic mapper imagery, of two physiologically different plant communities. The first is the Landes Forest, a coniferous region in south central France, during the June 1986 HAPEX-Mobilhy Experiment. The second is the semiarid Walnut Gulch basin of southeast Arizona that contains predominantly shrubs and grasses, during the June 1990 MONSOON Experiment. The procedure offers a physically based alternative to empirical vegetation indices for estimating regionally variable canopy densities of natural, homogeneous systems with little or no ground truth.

Sensitivity of the normalized difference vegetation index to subpixel canopy cover, soil albedo, and pixel scale.

Abstract The sensitivity of the normalized difference vegetation index (NDVI) to regional variations in the bulk subpixel properties of discontinuous plant canopies is investigated within the framework of a linear stochastic-geometric landsurface reflectance model. Analytical formulas are developed for i) the rate of change of the NDVI with respect to subpixel components and ii) the variance of the NDVI for an ensemble of pixels. Atmospheric effects are not considered. The formulas are first applied to the analysis of the NDVIs of a series of five simulated scenes of Poisson distributed plants, aggregated to three different pixel sizes. Varying only a single parameter in each subsequent scene provides an understanding of the influence of that variable on the behavior of the NDVI. Next, a comparison is made between the actual NDVI of a pecan orchard calculated from aerial radiometric data obtained during the June 1988 Maricopa Agricultural Center Experiment, and the predicted NDVI using the geometric reflectance model and ground truth. Finally, the NDVI of a natural landscape that possesses randomly distributed juniper trees and random soil background reflectance is investigated. Investigations are generalized to other plant geometries and solar angles through the use of a nondimensional similarity parameter η. The functional relation among the amount of canopy cover, shadowed ground, and illuminated ground, which occurs only for spatially homogeneous plant distributions at large sampling scales, facilitates the analytical treatment of the NDVI and reflectance equations.

Estimation of subpixel vegetation cover using red-infrared scattergrams

The bulk properties of discontinuous vegetation canopies are estimated at subpixel scales by applying the method of moments to a linear stochastic geometric model of canopy-soil reflectance and one set of multispectral observations without ground truth. The procedure involves the formulation of conditional moments for subsets of pixels that possess similar properties and can be identified through their common orientation in red-infrared scattergrams. The analysis is facilitated by assuming geometric similarity among the canopy elements and by formulating a sampling scale ratio in terms of the bulk geometric scales of the canopy and the pixel. Three versions of the method are demonstrated using two simulated scenes and an actual forested watershed for which aerial radiometric data and corresponding ground truth were obtained. >

Assimilation of Gridded GRACE Terrestrial Water Storage Estimates in the North American Land Data Assimilation System

AbstractThe objective of the North American Land Data Assimilation System (NLDAS) is to provide best-available estimates of near-surface meteorological conditions and soil hydrological status for the continental United States. To support the ongoing efforts to develop data assimilation (DA) capabilities for NLDAS, the results of Gravity Recovery and Climate Experiment (GRACE) DA implemented in a manner consistent with NLDAS development are presented. Following previous work, GRACE terrestrial water storage (TWS) anomaly estimates are assimilated into the NASA Catchment land surface model using an ensemble smoother. In contrast to many earlier GRACE DA studies, a gridded GRACE TWS product is assimilated, spatially distributed GRACE error estimates are accounted for, and the impact that GRACE scaling factors have on assimilation is evaluated. Comparisons with quality-controlled in situ observations indicate that GRACE DA has a positive impact on the simulation of unconfined groundwater variability across th...

Functional relation among subpixel canopy cover, ground shadow, and illuminated ground at large sampling scales

The functional relation among subpixel canopy cover, illuminated soil, and shadowed soil, which progressively develops with increasing pixel size, is investigated for Poisson distributed plants using a geometric canopy simulation model. An analytical relation among cover components is shown to be applicable when the scale of the pixel is much larger than the scale of the plant and ground shadow. The analysis is facilitated through the use of a nondimensional solar-geometric similarity parameter, r, equal to the ratio of the area of one plant canopy to its associated ground shadow area, as viewed from nadir. Use of the similarity parameter generalizes the results without constraining them to any one geometric shape or solar angle. A Sampling Scale Ratio, defined as the ratio of the area of the pixel to the mean area of a single plant shadow, is tested as a quantitative criterion to evaluate when the functional relation among subpixel components occurs. The results of a remote sensing experiment over a natural conifer landscape provide preliminary confirmation of the theoretical analysis.

Equations for the Drag Force and Aerodynamic Roughness Length of Urban Areas with Random Building Heights

We use a conceptual model to investigate how randomly varying building heights within a city affect the atmospheric drag forces and the aerodynamic roughness length of the city. The model is based on the assumptions regarding wake spreading and mutual sheltering effects proposed by Raupach (Boundary-Layer Meteorol 60:375–395, 1992). It is applied both to canopies having uniform building heights and to those having the same building density and mean height, but with variability about the mean. For each simulated urban area, a correction is determined, due to height variability, to the shear stress predicted for the uniform building height case. It is found that u*/u*R, where u* is the friction velocity and u*R is the friction velocity from the uniform building height case, is expressed well as an algebraic function of λ and σh/hm, where λ is the frontal area index, σh is the standard deviation of the building height, and hm is the mean building height. The simulations also resulted in a simple algebraic relation for z0/z0R as a function of λ and σh/hm, where z0 is the aerodynamic roughness length and z0R is z0 found from the original Raupach formulation for a uniform canopy. Model results are in keeping with those of several previous studies.

Sensitivity of a Floodplain Hydrodynamic Model to Satellite-Based DEM Scale and Accuracy: Case Study—The Atchafalaya Basin

The hydrodynamics of low-lying riverine floodplains and wetlands play a critical role in hydrology and ecosystem processes. Because small topographic features affect floodplain storage and flow velocity, a hydrodynamic model setup of these regions imposes more stringent requirements on the input Digital Elevation Model (DEM) compared to upland regions with comparatively high slopes. This current study provides a systematic approach to evaluate the required relative vertical accuracy and spatial resolution of current and future satellite-based altimeters within the context of DEM requirements for 2-D floodplain hydrodynamic models. A case study is presented for the Atchafalaya Basin with a model domain of 1190 km2. The approach analyzes the sensitivity of modeled floodplain water elevation and velocity to typical satellite-based DEM grid-box scale and vertical error, using a previously calibrated version of the physically-based flood inundation model (LISFLOOD-ACC). Results indicate a trade-off relationship between DEM relative vertical error and grid-box size. Higher resolution models are the most sensitive to vertical accuracy, but the impact diminishes at coarser resolutions because of spatial averaging. The results provide guidance to engineers and scientists when defining the observation scales of future altimetry missions such as the Surface Water and Ocean Topography (SWOT) mission from the perspective of numerical modeling requirements for large floodplains of O[103] km2 and greater.

NCA-LDAS land analysis: Development and performance of a multisensor, multivariate land data assimilation system for the National Climate Assessment

AbstractThis article describes one of the first successful examples of multisensor, multivariate land data assimilation, encompassing a large suite of soil moisture, snow depth, snow cover, and irr...

Inland and Near-Shore Water Profiles Derived from the High-Altitude Multiple Altimeter Beam Experimental Lidar (MABEL)

ABSTRACT Jasinski, M.; Stoll, J.; Cook, W.; Ondrusek, M.; Stengel, E., and Brunt, K., 2016. Inland and near-shore water profiles derived from the high-altitude Multiple Altimeter Beam Experiemental Lidar (MABEL). In: Brock, J.C.; Gesch, D.B.; Parrish, C.E.; Rogers, J.N., and Wright, C.W. (eds.), Advances in Topobathymetric Mapping, Models, and Applications. Journal of Coastal Research, Special Issue, No. 76, pp. 44–55. Coconut Creek (Florida), ISSN 0749-0208. The Advanced Topographic Laser Altimeter System (ATLAS) on the Ice, Cloud, and Land Elevation Satellite (ICESat-2) mission is a six beam, low energy, high repetition rate, 532-nm laser transmitter with photon counting detectors. Although designed primarily for detecting height changes in ice caps, sea ice, and vegetation, the polar-orbiting satellite will observe global surface water during its designed three-year life span, including inland water bodies, coasts, and open oceans. In preparation for the mission, an ICESat-2 prototype, the Multiple Altimeter Beam Experimental Lidar (MABEL), was built and flown on high-altitude aircraft experiments over a range of inland and near-shore targets. The purpose was to test the ATLAS concept and to provide a database for developing an algorithm that detects along track surface water height and light penetration under a range of atmospheric and water conditions. The current analysis examines the datasets of three MABEL transects observed from 20 km above ground of coastal and inland waters conducted in 2012 and 2013. Transects ranged from about 2 to 12 km in length and included the middle Chesapeake Bay, the near-shore Atlantic coast at Virginia Beach, and Lake Mead. Results indicate MABELs high capability for retrieving surface water height statistics with a mean height precision of approximately 5–7 cm per 100-m segment length. Profiles of attenuated subsurface backscatter, characterized using a Signal to Background Ratio written in Log10 base, or LSBR0, were observed over a range of 1.3 to 9.3 m, depending on water clarity and atmospheric background. Results indicate that observable penetration depth, although primarily dependent on water properties, was greatest when the solar background rate was low. Near-shore bottom reflectance was detected only at the Lake Mead site down to a maximum of 10 m under a clear night sky and low turbidity of approximately 1.6 Nephelometric Turbidity Units (NTU). The overall results suggest that the feasibility of retrieving operational surface water height statistics from space-based photon counting systems such as ATLAS is very high for resolutions down to about 100 m, even in partly cloudy conditions. The capability to observe subsurface backscatter profiles is achievable but requires much longer transects of several hundreds of meters.