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# Sentinel-2 L2A 120m Mosaic

![Header Thumbnail](/data/public-data/other-datasets/world-mosaic-2020.webp)

The Sentinel-2 L2A 120m mosaic is a derived product that provides the "best pixel" values for 10-daily periods. It is modeled by removing cloudy pixels and performing linear interpolation among the remaining valid observations. While designed to be cloud-free, some clouds may remain in regions with persistent, lengthy cloudy periods.

## Data Availability & Collections

The mosaic is split into annual collections with different band configurations.

* 2020 Collection: Contains 12 spectral bands and 1 quality mask.

  * **Collection ID**: `484d8dbb-9e3e-41f2-b96b-35189d3ae37f`

* 2019 Collection: Contains 6 spectral bands.

  * **Collection ID**: `0074520d-bcf5-4811-8f6f-afd946e77695`

## Basic Facts

| Property               | Value                                                     |
| ---------------------- | --------------------------------------------------------- |
| **Sensor**             | MultiSpectral Instrument (MSI) from Sentinel-2            |
| **Spatial Resolution** | 120 m                                                     |
| **Coordinate System**  | UTM                                                       |
| **Data Format**        | Cloud Optimized GeoTIFF (COG)                             |
| **Temporal Coverage**  | 2019, 2020 (Annual updates)                               |
| **License**            | [CC-BY 4.0](https://creativecommons.org/licenses/by/4.0/) |
| **Provider**           | **Planet**                                                |

## Band Information (2019 Product)

The 2019 mosaic includes the following 6 bands, typically provided in Digital Numbers (DN) ranging from 0 to 10,000.

| Name | Description | Resolution |
| ---- | ----------- | ---------- |
| B02  | Blue        | 120 m      |
| B03  | Green       | 120 m      |
| B04  | Red         | 120 m      |
| B08  | NIR         | 120 m      |
| B11  | SWIR 1      | 120 m      |
| B12  | SWIR 2      | 120 m      |

## Quality Mask (QM)

The `QM` band is essential for identifying the reliability of the interpolated data. It is recommended to filter data where `QM != 0`.

| Value | Meaning              | Description                                                    |
| ----- | -------------------- | -------------------------------------------------------------- |
| 0     | No Data              | Areas where no valid observations were found.                  |
| 1     | Interpolation Passed | Areas where the interpolation successfully finished.           |
| 2     | Artificially Raised  | DN values raised from 0 to 1 to avoid confusion with NO\_DATA. |
| 3     | Interpolation Failed | Detected persistent clouds; values set to maximum (10,000).    |

## Accessing the Data

### AWS S3 Access

The data is hosted on AWS in the `eu-central-1` region. You can list objects using the AWS CLI without an account:

```
aws s3 ls --no-sign-request s3://sentinel-s2-l2a-mosaic-120/2019/
```

Path Structure: `[year]/[month]/[day]/[UTM_code][latitude_band]/`

### Planet Insights Platform API

To access the data programmatically via the [Planet Insights Platform](https://insights.planet.com/):

* Endpoint: `services.sentinel-hub.com`

* Collection Type: `byoc-[Collection_ID]`

## Band Information (2020 Product)

The 2020 mosaic contains the full spectral range of Sentinel-2.

| Name        | Description      | Resolution |
| ----------- | ---------------- | ---------- |
| **B01**     | Coastal aerosol  | 120 m      |
| **B02**     | Blue             | 120 m      |
| **B03**     | Green            | 120 m      |
| **B04**     | Red              | 120 m      |
| **B05-B07** | Red Edge         | 120 m      |
| **B08/B8A** | NIR / Narrow NIR | 120 m      |
| **B09**     | Water Vapour     | 120 m      |
| **B11/B12** | SWIR 1 / SWIR 2  | 120 m      |
| **QM**      | Quality Mask     | 120 m      |

### Custom Scripts: Interpolated Time-Series

For users wanting to recreate or customize this mosaic, an **Interpolated Time-series** script is available. This script:

1. Defines a start and end date (for example, a full year).

2. Splits the timeframe into equal 10-daily intervals.

3. Applies cloud masking using `CLM` and `CLP` bands.

4. Performs linear interpolation to fill gaps caused by cloud cover.

**Example Evalscript Snippet:**

```
// VERSION=3

// Basic linear interpolation logic used for the 120m mosaic

function linearInterpolation(x, x0, y0, x1, y1) {

  var a = (y1 - y0) / (x1 - x0);

  var b = -a * x0 + y0;

  return a * x + b;

}
```

## Attribution

Contains modified Copernicus Sentinel data \[Year] processed by Sentinel Hub. For citations, use: Sentinel-2 L2A 120m Mosaic was accessed on \[DATE] from <https://registry.opendata.aws/sentinel-s2-l2a-mosaic-120>.