> 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-1b-products.md).

# Level-1B Products

At Level-1B, we introduce additional processing to make the measurements easier to analyze and compare.

## Key Details

* [x] Builds on Level-1A with additional radiometric and geometric processing
* [x] Pixel values represent top-of-atmosphere (TOA) reflectance and brightness temperature
* [x] VNIR and LWIR data are co-registered and aligned on a common 30 m grid
* [x] Nighttime LWIR data available

## Access

Level-1B products are distributed in two separate STAC collections to reflect differences in acquisition mode. The first collection includes both VNIR and thermal data from daytime acquisitions, while the second includes only thermal data from nighttime acquisitions.

You can access and explore these collections 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="350.55078125">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-1B Combined Thermal &#x26; VNIR Data</td><td><code>vz-l1b</code></td><td><span data-option="X5SCApiuC9oh">Daytime</span></td></tr><tr><td>Level-1B Thermal Data (Nighttime)</td><td><code>vz-l1b-night</code></td><td><span data-option="Dw5T3x8V9AWU">Nighttime</span></td></tr></tbody></table>

## Data & Metadata

Each Level-1B item includes multiple STAC assets, including cloud-optimized geoTIFFs (COGs) along with ancillary metadata and quality information.

{% hint style="warning" %}
Because Level-1B products are published in separate daytime and nighttime collections, each collection exposes only the subset of assets relevant to that acquisition mode. For details, see the `Availability` column.
{% endhint %}

<table data-search="false"><thead><tr><th width="188.1953125">Asset</th><th width="309.07421875">Description</th><th width="111.16796875">File Type<select><option value="3dK0BqQftPBM" label="COG" color="blue"></option><option value="Rq3yBois12ha" label="PNG" color="blue"></option><option value="hV68Nh64l6wP" label="JSON" color="blue"></option></select></th><th>Availability<select multiple><option value="EGTxnloDfylu" label="vz-l1b" color="blue"></option><option value="12yOXRbCQSva" label="vz-l1b-night" color="blue"></option></select></th></tr></thead><tbody><tr><td><code>BLUE</code></td><td>Blue TOA reflectance</td><td><span data-option="3dK0BqQftPBM">COG</span></td><td><span data-option="EGTxnloDfylu">vz-l1b</span></td></tr><tr><td><code>GREEN</code></td><td>Green TOA reflectance</td><td><span data-option="3dK0BqQftPBM">COG</span></td><td><span data-option="EGTxnloDfylu">vz-l1b</span></td></tr><tr><td><code>RED</code></td><td>Red TOA reflectance</td><td><span data-option="3dK0BqQftPBM">COG</span></td><td><span data-option="EGTxnloDfylu">vz-l1b</span></td></tr><tr><td><code>REDEDGE1</code></td><td>Red edge 1 TOA reflectance</td><td><span data-option="3dK0BqQftPBM">COG</span></td><td><span data-option="EGTxnloDfylu">vz-l1b</span></td></tr><tr><td><code>REDEDGE2</code></td><td>Red edge 2 TOA reflectance</td><td><span data-option="3dK0BqQftPBM">COG</span></td><td><span data-option="EGTxnloDfylu">vz-l1b</span></td></tr><tr><td><code>REDEDGE3</code></td><td>Red edge 3 TOA reflectance</td><td><span data-option="3dK0BqQftPBM">COG</span></td><td><span data-option="EGTxnloDfylu">vz-l1b</span></td></tr><tr><td><code>NIR</code></td><td>NIR TOA reflectance</td><td><span data-option="3dK0BqQftPBM">COG</span></td><td><span data-option="EGTxnloDfylu">vz-l1b</span></td></tr><tr><td><code>LWIR1</code></td><td>LWIR 1 brightness temperature</td><td><span data-option="3dK0BqQftPBM">COG</span></td><td><span data-option="EGTxnloDfylu">vz-l1b, </span><span data-option="12yOXRbCQSva">vz-l1b-night</span></td></tr><tr><td><code>LWIR2</code></td><td>LWIR 2 brightness temperature</td><td><span data-option="3dK0BqQftPBM">COG</span></td><td><span data-option="EGTxnloDfylu">vz-l1b, </span><span data-option="12yOXRbCQSva">vz-l1b-night</span></td></tr><tr><td><code>CLOUD_MASK</code></td><td>Cloud mask</td><td><span data-option="3dK0BqQftPBM">COG</span></td><td><span data-option="EGTxnloDfylu">vz-l1b</span></td></tr><tr><td><code>QUALITY_ASSURANCE</code></td><td>Radiometric saturation mask</td><td><span data-option="3dK0BqQftPBM">COG</span></td><td><span data-option="EGTxnloDfylu">vz-l1b, </span><span data-option="12yOXRbCQSva">vz-l1b-night</span></td></tr><tr><td><code>PREVIEW</code></td><td>Full-resolution preview image</td><td><span data-option="3dK0BqQftPBM">COG</span></td><td><span data-option="EGTxnloDfylu">vz-l1b, </span><span data-option="12yOXRbCQSva">vz-l1b-night</span></td></tr><tr><td><code>THUMBNAIL</code></td><td>Low-resolution thumbnail</td><td><span data-option="Rq3yBois12ha">PNG</span></td><td><span data-option="EGTxnloDfylu">vz-l1b, </span><span data-option="12yOXRbCQSva">vz-l1b-night</span></td></tr><tr><td><code>MTA</code></td><td>Ancillary metadata file</td><td><span data-option="hV68Nh64l6wP">JSON</span></td><td><span data-option="EGTxnloDfylu">vz-l1b, </span><span data-option="12yOXRbCQSva">vz-l1b-night</span></td></tr></tbody></table>

The ancillary metadata file includes coefficients for converting Level-1B values back to radiance.&#x20;

* VNIR reflectance values can be converted to radiance by applying the per-band `LEVEL1_RADIANCE_SCALING` coefficient.
* LWIR brightness temperature values can be converted to radiance as L = K<sub>1</sub>/(e(K<sub>2</sub>/BT)-1), where K<sub>1</sub> and K<sub>2</sub> are per-band `LEVEL1_BT_TO_RADIANCE_CONSTANTS`.

## Specifications

<table data-header-hidden><thead><tr><th width="221">Item</th><th valign="top">Level-1B</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>Resampling Method</strong></td><td valign="top">Bilinear</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">VNIR: 0.0001<br>LWIR: 0.01</td></tr></tbody></table>

## Processing

At Level-1B, we apply additional radiometric and geometric processing. These steps include:

* Conversion of radiance to TOA reflectance and brightness temperature
* Co-registration of VNIR and LWIR imagery on a common 30 m grid
* Orthorectification using a digital elevation model to improve geometric accuracy
* Cloud mask generation for identifying cloudy pixels
* Resampling and clipping to produce a common spatial footprint for all bands