Landscape Interpretation – Ilwaco, WA

Landscape Interpretation


Landscape Interpretation

Ilwaco, WA


Shane Canyon Walsh

Rowan University

Remote Sensing / Air Photo Interpretation
09 November 2016




Location:  Ilwaco, WA, the Columbia River and the Pacific Ocean.  Ilwaco, Washington, is located at 46.02984 decimal degrees north and 123.8889 decimal degrees west.  Ilwaco is a small town on the southwest coast of Washington state, where Washington borders the state of Oregon.  The Columbia River flows west towards the Pacific Ocean acting as a natural border between the two states.  Ilwaco has just under 1000 residents.  The town is roughly 17 miles northwest of Astoria, OR, the nearest major town, and 100 miles northwest of Portland, OR, the nearest major city.

Physical Features:  The physical features present are peninsulas, jetties, spits, islands, forests, beaches, harbors, lakes, rivers and ocean.

Land Covers:  The types of land cover present are open water, low intensity residential, commercial/industrial/transportation, shrubland, forested upland, barren and transitional.

Elevation:  The elevation ranges from 0 meters at sea level to 125 meters, at its highest point in the scene.

Source:  I downloaded the Landsat 8 Operational Land Imager (OLI) and Thermal Infrared Sensor (TIRS) data dated 19 Aug 2016, at  I downloaded the ASTER Digital Elevation Map (DEM) data dated 17 Oct 2011 (two files in order to Mosaic), at

Normalized Difference Vegetation Index (NDVI):  NDVI is a way of determining how green or lush a particular area is.  The images are taken from a satellite and the range of NDVI is calculated by the ratio of how much visible (VIS) and near-infrared light (NIR) is absorbed and reflected in the scene.  The equation to calculate NDVI is (NIR-VIS) / (NIR+VIS).  The range of NDVI for the scene is -.28 to .90.  The thresholds used were -.28 to .27, which indicated water, .27 to .70, which indicated no vegetation, .70 to .80, which indicated low vegetation and .80 to .90 for the high vegetation.  In the scene 171.63 square kilometers were water, 15.39 square kilometers had no vegetation, 17.63 square kilometers had low vegetation and 20.35 square kilometers had high vegetation.  76.28% of the scene was water, 6.84% had no vegetation, 7.84% had low vegetation and 9.04% had high vegetation.

Water:  To determine where water is in a given scene, two approaches are used.  The first is the Kauth-Thomas Tasseled-Cap Index, which uses combinations of readings to determine the wetness of the soil.  The range of Kauth-Thomas wetness in the scene is described as -.28 to .42.  The second approach is to construct a runoff model to see where the minor and major water pathways are.  The patterns of these minor and major pathways do not follow any general direction in the cape/peninsula, due in part to the elevation and the slimness of the land.  A drop of water will run off to the west or east depending on which side of the hill it lands on.  In the other areas not on the cape, the water appears to come down from the higher elevations toward the river or ocean.

Summary:  This type of study is useful as a way to determine sets of information about an area in particular.  This study was a first step to answering more questions.  Taken further, slope and aspect could be determined.  This would aid in deciding where to put an observation tower, for instance, over-looking the Pacific Ocean, while still being able to see the Columbia River, as well as having the least physical walk up.




Figure 1 – True color composite of Ilwaco, WA, the Columbia River and the Pacific Ocean


Figure 2 – ASTER Digital Elevation Map of Ilwaco, WA, The Columbia River and the Pacific Ocean


Figure 3 – Continuous NDVI for Ilwaco, WA, the Columbia River, and the Pacific Ocean


Figure 4 – Discrete NDVI for Ilwaco, WA, the Columbia River, and the Pacific Ocean


Figure 5 – NDVI values, including minimum and maximum values


Figure 6 – Kauth-Thomas wetness image with major and minor streams