Dean Whitman

A progressive morphological filter for removing nonground measurements from airborne LIDAR data

Recent advances in airborne light detection and ranging (LIDAR) technology allow rapid and inexpensive measurements of topography over large areas. This technology is becoming a primary method for generating high-resolution digital terrain models (DTMs) that are essential to numerous applications such as flood modeling and landslide prediction. Airborne LIDAR systems usually return a three-dimensional cloud of point measurements from reflective objects scanned by the laser beneath the flight path. In order to generate a DTM, measurements from nonground features such as buildings, vehicles, and vegetation have to be classified and removed. In this paper, a progressive morphological filter was developed to detect nonground LIDAR measurements. By gradually increasing the window size of the filter and using elevation difference thresholds, the measurements of vehicles, vegetation, and buildings are removed, while ground data are preserved. Datasets from mountainous and flat urbanized areas were selected to test the progressive morphological filter. The results show that the filter can remove most of the nonground points effectively.

Space geodesy: Subsidence and flooding in New Orleans

It has long been recognized that New Orleans is subsiding and is therefore susceptible to catastrophic flooding. Here we present a new subsidence map for the city, generated from space-based synthetic-aperture radar measurements, which reveals that parts of New Orleans underwent rapid subsidence in the three years before Hurricane Katrina struck in August 2005. One such area is next to the Mississippi River–Gulf Outlet (MRGO) canal, where levees failed during the peak storm surge: the map indicates that this weakness could be explained by subsidence of a metre or more since their construction.

Comparison of Three Algorithms for Filtering Airborne Lidar Data

This paper compares three methods for removing non-ground measurements from airborne laser scanning data. These methods, including the elevation threshold with expanding window (ETEW), maximum local slope (MLS), and progressive morphological (PM) filters, analyze data points based on variations of local slope, and elevation. Low and high-relief data sets with various densities of trees, houses, and sand dunes were selected to test the filtering methods. The results show that all three methods can effectively remove most nonground points in both low-relief urban and high-relief forested areas. The PM filter generated the best result in coastal barrier island areas, whereas the other algorithms tended to remove the tops of steep sand dunes. Each method experienced various omission or commission errors, depending on the filtering parameters. Topographic slope is the most sensitive parameter for the three filtering methods.

Quantification of Beach Changes Caused by Hurricane Floyd Along Florida's Atlantic Coast Using Airborne Laser Surveys

Abstract Quantitative data on beach changes caused by coastal storms is critical to the understanding of coastal morphodynamics and mitigation of coastal erosion hazards. Recent advances in airborne LIDAR technology allow large-scale mapping of beach erosion, dune scarping, and overwash deposition with incredible detail. By comparing 40 km of beaches along the central Florida Atlantic coast surveyed before and after Hurricane Floyd in 1999, we found that most beaches experienced erosion; about −18 to +1 m3/m of sediment per unit shoreline length were removed or deposited. Beach erosion is not spatially uniform, and variations in magnitude occur three dimensionally. The high-density LIDAR data provided accurate information about shore changes both at small and large scales.

Mapping Shoreline Position Using Airborne Laser Altimetry

Abstract This paper examines the feasibility of using LIDAR surveys to update existing historical shoreline data sets by comparing contour shorelines and the high water line (HWL) at eight study locations in North and South Carolina. The analysis was based on airborne LIDAR topography and orthoimagery collected simultaneously during June 2000. The popular method of digitizing the wet-dry line from orthoimagery was used to measure the HWL. Contour shorelines were derived by using the previous high tide (HW), the mean high water datum (MHW), and the mean higher high water datum (MHHW) of nearby tide gauges. A method was developed to quantitatively compare the positions of the HWL and the contour shorelines in a GIS. The mean high water and mean higher high water contour shoreline positions were the best match to the high water line at 7 of 8 locations, and differed by less than 5.4 meters from the digitized high water line positions. This difference is well within the errors associated with past methods for measuring shoreline position. Therefore, it is deemed practical to use LIDAR data to estimate the HWL.

The Isostatic Residual Gravity Anomaly of the Central Andes, 12° to 29° S: A Guide to Interpreting Crustal Structure and Deeper Lithospheric Processes

The isostatic residual gravity field of the Central Andean Plateau region contains laterally continuous, elongated anomalies that reflect the tectonic and magmatic effects of oceanic subduction in the forearc and continental subduction in the backarc. On the western side of the Andes, the residual anomalies are similar to those found at many “Andean”-type subduction margins. In particular, a high-low residual anomaly pair coincident with the coast and the Peru-Chile trench marks the location when the Nazca plate underthrusts beneath western South America. This high-low anomaly couple is mirrored in the backarc by a similar couple that tracks the location of the eastward-vergent Principal Frontal Thrust and results from the westward, antithetic subduction of the Brazilian shield beneath the plateau. The residual high is situated in the Eastern Cordillera of Bolivia, and is caused by a combination of high-density basement rocks near the surface in the hanging wall of the thrust, and by local crustal underco...

An analysis on the urban heat island effect using radiosonde profiles and Landsat imagery with ground meteorological data in South Florida

ABSTRACT Decades-long effects of drainage and development in south Florida that began in early to mid-20th century have resulted in the loss of natural forested and rangelands, and expansion of agricultural and urban areas. This has brought a change in the thermalscape of the surrounding areas. Surface and atmospheric surface-layers become drier and warmer in anthropogenic land covers compared to natural ones, introducing an effect called the urban heat island. This study aims to analyse the spatial and temporal existence of the urban heat island on land surface and near-surface atmosphere during summer using land-use/land-cover data, surface-based weather station records, radiosonde profiles, and Landsat-5 Thematic Mapper images captured between 1970 and 2012 in south Florida. Urban cover increased by about 10% from 1974 to 2011. The station-based urban–rural temperature difference (Tu-r is about 4°C over the entire area of south Florida and Landsat-derived surface temperature difference is about 3°C in the Landsat-covered area. They both show temporal increase throughout the period at a rate higher than the rate of increase of global average temperature. A decreasing near-surface diurnal temperature range of about ‒1°C (p = 0.005) and increased lifting condensation level (>20 m) were detected from the Miami radiosonde. Satisfactory validation results of surface and near-surface temperature (Nash–Sutcliffe coefficient = 0.70, coefficient of determination = 0.79) from the eastern urban stations further substantiate the findings on urban heat islands explored by the observed data.

Electrical Resistivity Characterization of Anisotropy in the Biscayne Aquifer

Electrical anisotropy occurs when electric current flow varies with azimuth. In porous media, this may correspond to anisotropy in the hydraulic conductivity resulting from sedimentary fabric, fractures, or dissolution. In this study, a 28-electrode resistivity imaging system was used to investigate electrical anisotropy at 13 sites in the Biscayne Aquifer of SE Florida using the rotated square array method. The measured coefficient of electrical anisotropy generally ranged from 1.01 to 1.12 with values as high as 1.36 found at one site. The observed electrical anisotropy was used to estimate hydraulic anisotropy (ratio of maximum to minimum hydraulic conductivity) which ranged from 1.18 to 2.83. The largest values generally were located on the Atlantic Coastal Ridge while the lowest values were in low elevation areas on the margin of the Everglades to the west. The higher values of anisotropy found on the ridge may be due to increased dissolution rates of the oolitic facies of the Miami formation limestone compared with the bryozoan facies to the west. The predominate trend of minimum resistivity and maximum hydraulic conductivity was E-W/SE-NW beneath the ridge and E-W/SW-NE farther west. The anisotropy directions are similar to the predevelopment groundwater flow direction as indicated in published studies. This suggests that the observed anisotropy is related to the paleo-groundwater flow in the Biscayne Aquifer.

Developing Benthic Class Specific, Chlorophyll-a Retrieving Algorithms for Optically-Shallow Water Using SeaWiFS.

This study evaluated the ability to improve Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) chl-a retrieval from optically shallow coastal waters by applying algorithms specific to the pixels’ benthic class. The form of the Ocean Color (OC) algorithm was assumed for this study. The operational atmospheric correction producing Level 2 SeaWiFS data was retained since the focus of this study was on establishing the benefit from the alternative specification of the bio-optical algorithm. Benthic class was determined through satellite image-based classification methods. Accuracy of the chl-a algorithms evaluated was determined through comparison with coincident in situ measurements of chl-a. The regionally-tuned models that were allowed to vary by benthic class produced more accurate estimates of chl-a than the single, unified regionally-tuned model. Mean absolute percent difference was approximately 70% for the regionally-tuned, benthic class-specific algorithms. Evaluation of the residuals indicated the potential for further improvement to chl-a estimation through finer characterization of benthic environments. Atmospheric correction procedures specialized to coastal environments were recognized as areas for future improvement as these procedures would improve both classification and algorithm tuning.

Depth of Closure Derived from Airborne Laser Bathymetry

This study develops a method to identify the depth of closure using airborne laser bathymetric data, and compares the measured depth of closure with estimated depth of closures. Airborne laser data sets were collected before and after the 2004 hurricane season in southeast Florida. Estimated depth of closures in terms of wave data is compatible to the measured depth of closures. However, the estimated depth of closure is on average larger than was measured, especially in the southern end of the study area, which could be due to geologic influence. Further research is needed to determine if geology plays a critical role in the depth of closure at this studys location.