> For the complete documentation index, see [llms.txt](https://satdocs.hydrosat.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://satdocs.hydrosat.com/thermal-data/product-details/level-2-products.md).

# Level-2 Products

At Level-2, we estimate what's happening at Earth's surface rather than what the satellite directly observed.

## Key Details

* [x] Our highest-level imagery product
* [x] Pixel values represent surface reflectance (SR) and land surface temperature (LST)
* [x] Includes atmospheric, terrain, and surface corrections
* [x] Best suited for environmental monitoring and scientific analysis

## Access

A single Level-2 STAC collection is available. You can access and explore this collection via either the [Discovery portal](https://discover.hydrosat.com) or the [STAC API](/data-discovery-platform/stac-api-documentation.md).

<table><thead><tr><th width="366.578125">Collection Name</th><th>Collection ID</th><th>Imaging Time<select><option value="FYAq5teYqZma" label="vz-viri-l1a" color="blue"></option><option value="EWecW3jOmwZt" label="vz-liri-l1a-night" color="blue"></option><option value="FtHXeinPQD91" label="vz-liri-l1a" color="blue"></option><option value="X5SCApiuC9oh" label="Daytime" color="blue"></option><option value="Dw5T3x8V9AWU" label="Nighttime" color="blue"></option></select></th></tr></thead><tbody><tr><td>Level-2 Surface Temperature &#x26; Surface Reflectance Data</td><td><code>vz-l2</code></td><td><span data-option="X5SCApiuC9oh">Daytime</span></td></tr></tbody></table>

## Data & Metadata

All of the following assets are available for every Level-2 item, since Level-2 products are distributed in a single STAC collection.

<table data-search="false"><thead><tr><th width="191.99609375">Asset</th><th width="438.12109375">Description</th><th>File Type<select><option value="3tframT0ionq" label="COG" color="blue"></option><option value="JEMKsYbGLJVS" label="PNG" color="blue"></option><option value="B1x1N2vNWRwo" label="JSON" color="blue"></option></select></th></tr></thead><tbody><tr><td><code>LST</code></td><td>Land surface temperature</td><td><span data-option="3tframT0ionq">COG</span></td></tr><tr><td><code>BLUE_SR</code></td><td>Blue surface reflectance</td><td><span data-option="3tframT0ionq">COG</span></td></tr><tr><td><code>GREEN_SR</code></td><td>Green surface reflectance</td><td><span data-option="3tframT0ionq">COG</span></td></tr><tr><td><code>RED_SR</code></td><td>Red surface reflectance</td><td><span data-option="3tframT0ionq">COG</span></td></tr><tr><td><code>REDEDGE1_SR</code></td><td>Red edge 1 surface reflectance</td><td><span data-option="3tframT0ionq">COG</span></td></tr><tr><td><code>REDEDGE2_SR</code></td><td>Red edge 2 surface reflectance</td><td><span data-option="3tframT0ionq">COG</span></td></tr><tr><td><code>REDEDGE3_SR</code></td><td>Red edge 3 surface reflectance</td><td><span data-option="3tframT0ionq">COG</span></td></tr><tr><td><code>NIR_SR</code></td><td>NIR surface reflectance</td><td><span data-option="3tframT0ionq">COG</span></td></tr><tr><td><code>LWIR1_EMIS</code></td><td>LWIR 1 emissivity</td><td><span data-option="3tframT0ionq">COG</span></td></tr><tr><td><code>LWIR2_EMIS</code></td><td>LWIR 2 emissivity</td><td><span data-option="3tframT0ionq">COG</span></td></tr><tr><td><code>LST_UNCERTAINTY</code></td><td>Land surface temperature uncertainty</td><td><span data-option="3tframT0ionq">COG</span></td></tr><tr><td><code>CLOUD_MASK</code></td><td>Cloud mask</td><td><span data-option="3tframT0ionq">COG</span></td></tr><tr><td><code>QUALITY_ASSURANCE</code></td><td>Radiometric saturation mask</td><td><span data-option="3tframT0ionq">COG</span></td></tr><tr><td><code>PREVIEW</code></td><td>Full-resolution preview image</td><td><span data-option="3tframT0ionq">COG</span></td></tr><tr><td><code>THUMBNAIL</code></td><td>Low-resolution thumbnail</td><td><span data-option="JEMKsYbGLJVS">PNG</span></td></tr><tr><td><code>METADATA</code></td><td>Ancillary metadata file</td><td><span data-option="B1x1N2vNWRwo">JSON</span></td></tr></tbody></table>

## Specifications

<table data-header-hidden><thead><tr><th width="221">Item</th><th valign="top">Details</th></tr></thead><tbody><tr><td><strong>Scene Size</strong></td><td valign="top">70 km x 70 km</td></tr><tr><td><strong>Pixel Size</strong></td><td valign="top">30 m</td></tr><tr><td><strong>Map Projection</strong></td><td valign="top">Universal Transverse Mercator (UTM)</td></tr><tr><td><strong>No Data Value</strong></td><td valign="top">0</td></tr><tr><td><strong>Scale Factor</strong></td><td valign="top"><p>LST &#x26; LST uncertainty: 0.01</p><p>Surface reflectance &#x26; emissivity: 0.0001</p></td></tr></tbody></table>

## Processing

At Level-2, we apply the processing needed to derive surface reflectance and land surface temperature. This is an involved sequence that includes:

* Radiometric terrain correction to account for terrain-induced illumination effects
* Surface reflectance retrieval from TOA reflectance
* LST estimation from TOA brightness temperatures with emissivity correction
* Per-pixel LST uncertainty estimation based on radiometric, emissivity, atmospheric, and algorithm uncertainties