Data Acquisition

Home » Research » Environmental Studies » LULC Change in Carroll County » Methodology » Data Acquisition

Other Methodology areas:

Loading, please wait...

Chapter 4 - Methodology

Data Acquisition

Landsat Thematic Mapper (TM) Imagery

Landsat Thematic Mapper imagery constitutes the base data layer from which the land use and land cover maps were derived. The scope of this study required the acquisition of four system corrected Landsat TM scenes. (Table 4.1) System corrected refers to the corrections performed at the ground receiving station based on previously known sensor (system) distortions such as the pitch, roll, and velocity of the satellite platform (Smith, et al., 1998).

Table 4.1 Landsat TM Scenes

The appropriate selection of imagery acquisition dates for change detection is an integral component of a projects success. Anniversary dates or within anniversary windows have become commonplace in change detection studies because they minimize discrepancies in reflectance caused by seasonal vegetation fluxes and sun angle differences (Coppin & Bauer, 1996). The following criteria were considered during the selection of available TM scenes:

1: Forest cover phenological stability associated with similar temporal characteristics

2: Lowest possible seasonal moisture content

3: Minimum sun angle effects, minimum variation in solar zenith angles between dates in this window

4: Lowest percent monthly cloud cover, based on the examination of the Landsat TM imagery available for the study area since 1982

The acquisition dates of the TM Scenes employed in the change detection process fall within an acceptable anniversary window: September 18th, 1984 and October 6th, 1999, a difference of 18 days.

Hame (1988) concluded that for change detection, summer and winter are the best seasons because of their phenological stability. Selecting the summer, or driest period of the year for the locale, will enhance spectral separability, yet minimize spectral similarity due to excessive wetness prevailing during other periods of the year (Burns & Joyce, 1981). The TM scenes selected also coincide with these issues, opting for the best potential results.

The first scene was obtained by means of a grant from the University of Arkansas Graduate School as part of the Arkansas Space Grant Consortium on behalf of Dr. Collis Geren, Dean of Graduate School, Dr. John Hehr, Associate Dean of Fulbright College of Arts and Sciences, and Phil Stafford of the Arkansas Space Grant Consortium. The funds were distributed from National Science Foundation, NSF, and Experimental Program to Stimulate Cooperative Research, EPScOR, grants. The image was acquired from the EROS, Earth Resource Observing System, Data Center in Sioux Falls, South Dakota, an entity of the U.S. Geological Service. This TM scene, World Reference System Path/Row 25/35, was captured by the Landsat 5 satellite on September 18, 1984.

The second, third and fourth TM scenes were acquired from the data archives at The Center for Advanced Spatial Technologies (CAST). Utilization of these scenes was authorized and approved by Dr. Fred Limp, CAST Director, and Bruce Gorham, Remote Sensing/GIS Specialist, CAST. These images were originally obtained from the EROS Data Center as part of a state-wide imagery purchase for an on-going 1999 Arkansas Land Use and Land Cover Project by CAST. The TM scenes, WRS Path/Row 25/35, were captured by the Landsat 7 satellite on May 7, October 6, and December 25, 1999 respectively. All Landsat scenes were screened for system error and cloud cover prior to acquisition.

U.S. Geological Survey Digital Elevation Model (DEM)

A 7.5 minute digital elevation model (DEM) of Carroll County was also obtained from the data archives of CAST. A digital elevation model consists of a sampled array of regularly spaced elevation values referenced horizontally to a geographic coordinate system. The 7.5 minute DEM has a profile of 30 meter square grid spacing along and between each profiles, grid columns and rows, (USGS, 1998). The 30 meter spatial resolution was essential in order to coincide with that of the Landsat TM imagery and classified land use and land cover maps.

Soil Survey Geographic Data, SSURGO

Soil Survey Geographic, SSURGO, Data, for Carroll County was obtained from U.S. Department of Agriculture’s (USDA) Natural Resources Conservation Service (NRCS) database on the World Wide Web in an Arc interchange format. The SSURGO soils data provides the most detailed level of information and was designed primarily for farm and ranch, landowner/user, township, county, or parish natural resource planning and management. This database serves as an excellent source for determining erodible areas, land use potential, and land use assessments (USDA, 1995).

Ancillary Vector Data

Arkansas Highway and Transportation Department (AHTD) and National Transportation Safety Board (NTSB) vector transportation data was also obtained from the data archives at CAST. The vector data for Carroll County included: the Carroll County boundary, city boundaries, U.S. Highways, State Highways, county roads, city roads, railroads, airports, lakes, rivers, and streams.

In addition, a 12 digit preliminary hydrologic watershed boundary of the Upper White River dataset was acquired from the Soil Physics Laboratory, Department of Agronomy at the University of Arkansas, Fayetteville in conjunction with the National Recourses Conservation Service. 12 digit refers to sub-watersheds ranging in size from 10,000 to 40,000 acres. Special permission was granted for the utilization of this preliminary dataset from Marty Mckimmey of the Soil Physics Laboratory.