ch6_b.qmd

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## Exercise #3

The Harmonized Landsat Sentinel-2 (HLS) project provides consistent multiband surface reflectance (SR) data from NASA/USGS Landsat 8 and Landsat 9 satellites (using Operational Land Imager, OLI) and Europe’s Copernicus Sentinel-2A and Sentinel-2B satellites (using Multi-Spectral Instrument, MSI).
These measurements provide global land observations with a 2–3 days temporal frequency at 30-meter spatial resolution.
Sample rasters for band 4 (Red) and band 5 (Near-Infrared) from this resource are provided at the following location in the sample data: "./SampleData-master/raster_files/landsat/"

For LANDSAT 8, the Normalized Difference Vegetation Index (a proxy for vegetation health) is calculated as:

$$
 NDVI=(Band 5- Band 4)/(Band 5+ Band 4)
$$ For more information on the HSL products, bands and applications, please refer to: <https://lpdaac.usgs.gov/data/get-started-data/collection-overview/missions/harmonized-landsat-sentinel-2-hls-overview/>

```{r ch6_b1, message = FALSE, warning = FALSE}
#| layout-ncol: 2

# Import surface reflectance bands
library(terra)
library(RColorBrewer)

b4=rast("./SampleData-master/raster_files/landsat/HLS.L30.T15RYP.2024055T163211.v2.0.B04.tif")
b5=rast("./SampleData-master/raster_files/landsat/HLS.L30.T15RYP.2024055T163211.v2.0.B05.tif")

# Plot rasters
plot(b4, main="Red band",col= brewer.pal(11,"BrBG"))
plot(b5, main="NIR band",col= brewer.pal(11,"BrBG"))
```

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Using the spectral band rasters provided above, complete the following objectives:

1.  \(10\) Generate and plot NDVI raster for the areal domain.
    \[HINT: Use multi-raster arithmetic from 4.1.2\]

2.  \(10\) Reproject the NDVI raster to the following projection: North American Datum 1983 (NAD83, refer to Sec 3.2.8 for help)

3.  \(10\) Clamp the range of the NDVI to \[-1,1\].
    \[Hint: Checkout the flash card at the end of chapter 4 or try ?t
    erra::clamp\]

4.  \(10\) Plot the reprojected NDVI raster and add the following locations of interest to the map \[Hint: Check out Sec 3.2.8\]:

    -   Location 1: Lon1=-90.6, Lat1= 30.4

    -   Location 2:Lon2=-90, Lat2= 30.1

5.  \(10\) Extract NDVI values for the two locations given above.
    \[Hint look at the example for extract in 6.3.1\]

6.  \(20\) Crop the NDVI raster to the following extent and plot the cropped raster: \[Xmin, Xmax, Ymin, Ymax\]= \[-90.5, -90.4, 30.05, 30.15\].
    \[HINT: Create a vector using the extent and use it for cropping\]

7.  \(30\) Use NASA Earth Data Search (as shown in Section 6.2.6) to download Harmonized Landsat Sentinel-2 (HLS) surface reflectance for band 4 and 5 for any date and region of your choice.
    Repeat objectives 1 through 3 and plot the resultant NDVI raster.