> 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-1a-products.md).

# Level-1A Products

At Level-1A, we provide the closest representation of what the satellite measured.

## Key Details

* [x] The least processed of Hydrosat's available imagery products
* [x] Pixel values represent at-sensor radiance in scaled units of W/m²/sr/µm
* [x] Preserves the native spatial resolution and swath of each sensor
* [x] Includes essential instrument-level corrections and georegistration
* [x] Nighttime LWIR data available

## Access

Level-1A products are available in three STAC collections: daytime VNIR, daytime LWIR, and nighttime LWIR. You can access and explore these collections via either the [Discovery portal](https://discover.hydrosat.com) (using the Collection dropdown) or the [STAC API](/data-discovery-platform/stac-api-documentation.md).

<table><thead><tr><th width="313.34765625">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-1A VNIR Data</td><td><code>vz-viri-l1a</code></td><td><span data-option="X5SCApiuC9oh">Daytime</span></td></tr><tr><td>Level-1A Thermal Data</td><td><code>vz-liri-l1a</code></td><td><span data-option="X5SCApiuC9oh">Daytime</span></td></tr><tr><td>Level-1A Thermal Data (Nighttime)</td><td><code>vz-liri-l1a-night</code></td><td><span data-option="Dw5T3x8V9AWU">Nighttime</span></td></tr></tbody></table>

## Data & Metadata

Each Level-1A item includes multiple STAC assets, including one cloud-optimized GeoTIFF (COG) for each spectral band.

{% hint style="warning" %}
Because VNIR and LWIR products are provided in separate Level-1A collections, each collection exposes only the subset of assets applicable to that sensor. For details, see the `Availability` column.
{% endhint %}

<table data-search="false"><thead><tr><th width="220.4921875">Asset Name</th><th width="266.22265625">Description</th><th width="113.8125">File Type<select><option value="4uUQ8vQbL2MX" label="COG" color="blue"></option><option value="0UZddAqx82hy" label="PNG" color="blue"></option><option value="Dh6mpinfrDQj" label="JSON" color="blue"></option></select></th><th>Availability<select multiple><option value="dnCj7YU44ok5" label="vz-viri-l1a" color="blue"></option><option value="QI2q3lCxbFrR" label="vz-liri-l1a" color="blue"></option><option value="aqc791Aiofam" label="vz-liri-l1a-night" color="blue"></option></select></th></tr></thead><tbody><tr><td><code>BLUE</code></td><td>Blue radiance</td><td><span data-option="4uUQ8vQbL2MX">COG</span></td><td><span data-option="dnCj7YU44ok5">vz-viri-l1a</span></td></tr><tr><td><code>GREEN</code></td><td>Green radiance</td><td><span data-option="4uUQ8vQbL2MX">COG</span></td><td><span data-option="dnCj7YU44ok5">vz-viri-l1a</span></td></tr><tr><td><code>RED</code></td><td>Red radiance</td><td><span data-option="4uUQ8vQbL2MX">COG</span></td><td><span data-option="dnCj7YU44ok5">vz-viri-l1a</span></td></tr><tr><td><code>REDEDGE1</code></td><td>Red edge 1 radiance</td><td><span data-option="4uUQ8vQbL2MX">COG</span></td><td><span data-option="dnCj7YU44ok5">vz-viri-l1a</span></td></tr><tr><td><code>REDEDGE2</code></td><td>Red edge 2 radiance</td><td><span data-option="4uUQ8vQbL2MX">COG</span></td><td><span data-option="dnCj7YU44ok5">vz-viri-l1a</span></td></tr><tr><td><code>REDEDGE3</code></td><td>Red edge 3 radiance</td><td><span data-option="4uUQ8vQbL2MX">COG</span></td><td><span data-option="dnCj7YU44ok5">vz-viri-l1a</span></td></tr><tr><td><code>NIR</code></td><td>NIR radiance</td><td><span data-option="4uUQ8vQbL2MX">COG</span></td><td><span data-option="dnCj7YU44ok5">vz-viri-l1a</span></td></tr><tr><td><code>LWIR1</code></td><td>LWIR1 radiance</td><td><span data-option="4uUQ8vQbL2MX">COG</span></td><td><span data-option="QI2q3lCxbFrR">vz-liri-l1a, </span><span data-option="aqc791Aiofam">vz-liri-l1a-night</span></td></tr><tr><td><code>LWIR2</code></td><td>LWIR2 radiance</td><td><span data-option="4uUQ8vQbL2MX">COG</span></td><td><span data-option="QI2q3lCxbFrR">vz-liri-l1a, </span><span data-option="aqc791Aiofam">vz-liri-l1a-night</span></td></tr><tr><td><code>QUALITY_ASSURANCE</code></td><td>Radiometric saturation mask</td><td><span data-option="4uUQ8vQbL2MX">COG</span></td><td><span data-option="dnCj7YU44ok5">vz-viri-l1a, </span><span data-option="QI2q3lCxbFrR">vz-liri-l1a, </span><span data-option="aqc791Aiofam">vz-liri-l1a-night</span></td></tr><tr><td><code>PREVIEW</code></td><td>Full-resolution preview image</td><td><span data-option="4uUQ8vQbL2MX">COG</span></td><td><span data-option="dnCj7YU44ok5">vz-viri-l1a, </span><span data-option="QI2q3lCxbFrR">vz-liri-l1a, </span><span data-option="aqc791Aiofam">vz-liri-l1a-night</span></td></tr><tr><td><code>THUMBNAIL</code></td><td>Low-resolution thumbnail</td><td><span data-option="0UZddAqx82hy">PNG</span></td><td><span data-option="dnCj7YU44ok5">vz-viri-l1a, </span><span data-option="QI2q3lCxbFrR">vz-liri-l1a, </span><span data-option="aqc791Aiofam">vz-liri-l1a-night</span></td></tr><tr><td><code>MTA</code></td><td>Ancillary metadata file</td><td><span data-option="Dh6mpinfrDQj">JSON</span></td><td><span data-option="dnCj7YU44ok5">vz-viri-l1a, </span><span data-option="QI2q3lCxbFrR">vz-liri-l1a, </span><span data-option="aqc791Aiofam">vz-liri-l1a-night</span></td></tr></tbody></table>

The ancillary metadata file includes, among other information, the coefficients that a user would need to convert radiance values to reflectance or brightness temperature.

* VNIR radiance values can be converted to top-of-atmosphere reflectance by applying the per-band `LEVEL1_REFLECTANCE_SCALING` coefficient.
* LWIR radiance values can be converted to brightness temperature as BT = K<sub>2</sub>/ln(K<sub>1</sub>/L+1), where K<sub>1</sub> and K<sub>2</sub> are per-band `LEVEL1_THERMAL_CONSTANTS`  and L represents scaled radiance.

## Specifications

<table><thead><tr><th width="221">Item</th><th valign="top">Level-1A VNIR</th><th>Level-1A LWIR</th></tr></thead><tbody><tr><td><strong>Scene Size</strong></td><td valign="top">122 km x 70 km</td><td>70 km x 70 km</td></tr><tr><td><strong>Pixel Size</strong></td><td valign="top">29.9 m</td><td>68.8 m</td></tr><tr><td><strong>Map Projection</strong></td><td valign="top">EPSG 4326</td><td>EPSG 4326</td></tr><tr><td><strong>No Data Value</strong></td><td valign="top">0</td><td>0</td></tr><tr><td><strong>Scale Factor</strong></td><td valign="top">0.01</td><td>0.001</td></tr></tbody></table>

## Processing

Only the most essential onboard and ground processing steps are applied at Level-1A. These include:

* Time delay integration (TDI) to combine multiple measurements and produce a cleaner image
* Non-uniformity correction to reduce variations in detector response
* Band coregistration to align the spectral bands within each sensor
* Georegistration to assign each pixel a geographic location
* Radiometric calibration to convert sensor measurements into radiance