Remote Sensing Project using GLOVIS/ArcGIS Pro

Question

I'm doing a project where I extract images from USGS/Glovis and analyze/process them with ARCGIS Pro do determine soil erosion on the coasts of Albania. I would like some help with retrieving this imagery from Glovis using temporal/historical observation and then process this in arcgis pro do determine the magnitude of erosion

Answer 1

To determine the magnitude of erosion, you will essentially be performing Shoreline Change Analysis. By comparing the position of the "shoreline" (the land-water interface) across different years, you can calculate the rate of retreat in meters per year.

Phase 1: Retrieving Imagery from GLOVIS

For a long-term study (1980s to present), Landsat is your best bet because of its historical depth. For higher resolution in recent years (2015–present), you can supplement with Sentinel-2.

1. Search Criteria: Log into USGS GloVis.
2. Select Dataset: Choose Landsat 8-9 OLI/TIRS C2 L1 for modern data and Landsat 4-5 TM or 7 ETM+ for historical data.
3. Filter by Date: To get a clear "temporal observation," pick one image per year (or every 5 years) from the same season (e.g., all images from August). This minimizes seasonal tide/vegetation variances.
4. Cloud Cover: Set this to < 10% to ensure the coastline isn't obscured.
5. Download: Download the Level-1 GeoTIFF files. You will need the individual spectral bands to process them in ArcGIS.

Phase 2: Processing in ArcGIS Pro

Once you have your images, you need to turn those "pictures" into "measurable lines."

1. Pre-Processing & Indexing

Instead of just looking at the image, use a Water Index to mathematically separate land from water.

1. NDWI (Normalized Difference Water Index): This highlights water bodies.
2. $$NDWI = \frac{Green - NIR}{Green + NIR}$$
3. In ArcGIS Pro: Use the Raster Calculator (Spatial Analyst tool) to apply this formula. In Landsat 8/9, this is $\frac{Band 3 - Band 5}{Band 3 + Band 5}$.

2. Extracting the Shoreline

1. Reclassify: Use the Reclassify tool on your NDWI result. Set a threshold (usually 0) where values above are water and below are land.
2. Raster to Polygon: Convert that reclassified raster into a polygon.
3. Polygon to Line: Use the Polygon to Line tool. The resulting line where land meets water is your "Shoreline" for that specific year.

Phase 3: Determining Magnitude of Erosion

To get the actual "magnitude" (e.g., -2 meters/year), you need to compare these lines.

1. Manual Measurement: You can use the Measure Tool to check the distance between your 1990 shoreline and your 2024 shoreline at specific points.
2. Professional Method (DSAS): Most researchers use the Digital Shoreline Analysis System (DSAS), a free tool from the USGS that works as an add-in. It automatically casts "transects" (perpendicular lines) every few meters along the coast and calculates:
3. NSM (Net Shoreline Movement): Total distance changed.
4. EPR (End Point Rate): The speed of erosion (distance divided by time).