Harmonizing Landsat and Sentinel Data

Oct 13, 2025 by wbrum.org 17 views

Introduction

The increasing availability of satellite data from various sources has revolutionized the field of remote sensing. Landsat and Sentinel-2 are two prominent satellite missions that provide high-resolution data for various applications, including land cover classification, crop monitoring, and climate change analysis. However, the data from these two sources are not directly compatible due to differences in spatial resolution, spectral bands, and acquisition dates. To overcome this limitation, the QA-band is used to harmonize Landsat and Sentinel data, enabling the creation of a single, consistent dataset for analysis. In this article, we will discuss how to use the QA-band for harmonized Landsat and Sentinel data to process the data for NDVI, NDWI, and LST analysis.

Understanding the QA-band

The QA-band is a critical component of the Harmonized Landsat and Sentinel-2 (HLS) data, which is available for download from NASA's AppEEARS (https://appeears.earthdatacloud.nasa.gov/task/area). The QA-band contains a set of flags that indicate the quality of the data, including the presence of clouds, shadows, and atmospheric conditions. By using the QA-band, users can identify and remove poor-quality data, ensuring that the resulting dataset is accurate and reliable.

Harmonizing Landsat and Sentinel Data

To harmonize Landsat and Sentinel data, we need to follow a series of steps:

Download the HLS data: The first step is to download the HLS data from NASA's AppEEARS. We can choose the desired dataset, including the spatial resolution, spectral bands, and acquisition dates.
Load the data into QGIS: Once the data is downloaded, we can load it into QGIS, a popular geographic information system (GIS) software.
Apply the QA-band: The next step is to apply the QA-band to the data. This involves creating a new raster layer that contains the QA-band flags.
Remove poor-quality data: Using the QA-band flags, we can identify and remove poor-quality data, including clouds, shadows, and atmospheric conditions.
Mosaic the data: Once the poor-quality data is removed, we can mosaic the remaining data to create a single, consistent dataset.

Processing the Data for NDVI, NDWI, and LST Analysis

After harmonizing the Landsat and Sentinel data, we can process the data for NDVI, NDWI, and LST analysis. Here are the steps:

NDVI Analysis

Calculate the NDVI: The first step is to calculate the NDVI (Normalized Difference Vegetation Index) using the near-infrared (NIR) and red bands.
Apply the QA-band: We can apply the QA-band flags to the NDVI data to remove poor-quality pixels.
Visualize the results: Finally, we can visualize the NDVI results using a color ramp or a histogram.

NDWI Analysis

Calculate the NDWI: The first step is to calculate the NDWI (Normalized Difference Water Index) using the green and NIR bands.
Apply the QA-band: We can apply the QA-band flags to the NDWI data to remove poor-quality pixels.
Visualize the results: Finally, we can visualize the NDWI results using a color ramp or a histogram.

LST Analysis

Calculate the LST: The first step is to calculate the LST (Land Surface Temperature) using the thermal infrared (TIR) band.
Apply the QA-band: We can apply the QA-band flags to the LST data to remove poor-quality pixels.
Visualize the results: Finally, we can visualize the LST results using a color ramp or a histogram.

Conclusion

In conclusion, the QA-band is a critical component of the HLS data, enabling the harmonization of Landsat and Sentinel data. By applying the QA-band flags, users can identify and remove poor-quality data, ensuring that the resulting dataset is accurate and reliable. This article has discussed how to use the QA-band for harmonized Landsat and Sentinel data to process the data for NDVI, NDWI, and LST analysis. By following the steps outlined in this article, users can create a single, consistent dataset for analysis, enabling a range of applications, including land cover classification, crop monitoring, and climate change analysis.

Future Work

Future work includes:

Improving the QA-band: The QA-band is a critical component of the HLS data, and improving its accuracy and reliability will be essential for future applications.
Developing new algorithms: New algorithms and techniques will be developed to improve the accuracy and efficiency of the data processing and analysis.
Integrating with other datasets: The HLS data will be integrated with other datasets, including climate and weather data, to enable a range of applications, including climate change analysis and crop monitoring.

References

NASA AppEEARS: https://appeears.earthdatacloud.nasa.gov/task/area
HLS data: https://landsat.gsfc.nasa.gov/hls/
QGIS: https://www.qgis.org/en/site/

Glossary

HLS: Harmonized Landsat and Sentinel-2 data
QA-band: Quality assurance band
NDVI: Normalized Difference Vegetation Index
NDWI: Normalized Difference Water Index
LST: Land Surface Temperature
TIR: Thermal Infrared band
NIR: Near-Infrared band
Red band: Red band
Green band: Green band

Q: What is the Harmonized Landsat and Sentinel-2 (HLS) data?

A: The HLS data is a dataset that combines the strengths of Landsat and Sentinel-2 satellite data, providing a consistent and high-quality dataset for various applications, including land cover classification, crop monitoring, and climate change analysis.

Q: What is the QA-band, and how is it used in HLS data?

A: The QA-band is a critical component of the HLS data, containing a set of flags that indicate the quality of the data, including the presence of clouds, shadows, and atmospheric conditions. By using the QA-band, users can identify and remove poor-quality data, ensuring that the resulting dataset is accurate and reliable.

Q: How do I download the HLS data from NASA's AppEEARS?

A: To download the HLS data from NASA's AppEEARS, follow these steps:

Go to the AppEEARS website (https://appeears.earthdatacloud.nasa.gov/task/area).
Select the desired dataset, including the spatial resolution, spectral bands, and acquisition dates.
Choose the desired output format and resolution.
Click on the "Download" button to download the data.

Q: How do I load the HLS data into QGIS?

A: To load the HLS data into QGIS, follow these steps:

Open QGIS and create a new project.
Go to the "Layer" menu and select "Add Raster Layer".
Navigate to the location where you downloaded the HLS data and select the file.
Click on the "Add" button to add the layer to the project.

Q: How do I apply the QA-band to the HLS data?

A: To apply the QA-band to the HLS data, follow these steps:

Open the HLS data in QGIS.
Go to the "Raster" menu and select "Band Calculator".
Enter the following expression: qa_band = if (qa_band == 1, 1, 0)
Click on the "OK" button to apply the QA-band.

Q: How do I remove poor-quality data using the QA-band?

A: To remove poor-quality data using the QA-band, follow these steps:

Open the HLS data in QGIS.
Go to the "Raster" menu and select "Band Calculator".
Enter the following expression: qa_band = if (qa_band == 1, 0, qa_band)
Click on the "OK" button to remove the poor-quality data.

Q: How do I calculate the NDVI, NDWI, and LST from the HLS data?

A: To calculate the NDVI, NDWI, and LST from the HLS data, follow these steps:

Open the HLS data in QGIS.
Go to the "Raster" menu and select "Band Calculator".
Enter the following expressions:
- NDVI: (nir - red) / (nir + red)
- NDWI: (green - nir) / (green + nir)
- LST: (tir - 273.15) / 0.02
Click on the "OK" button to calculate the indices.

Q: How do I visualize the results of the NDVI, NDWI, and LST analysis?

A: To visualize the results of the NDVI, NDWI, and LST analysis, follow these steps:

Open the results in QGIS.
Go to the "Layer" menu and select "Add Raster Layer".
Select the desired color ramp or histogram.
Click on the "OK" button to visualize the results.

Q: What are some common issues that may arise during the harmonization and analysis of HLS data?

A: Some common issues that may arise during the harmonization and analysis of HLS data include:

Cloud cover and shadows
Atmospheric conditions
Sensor calibration and registration
Data format and resolution

Q: How can I troubleshoot common issues during the harmonization and analysis of HLS data?

A: To troubleshoot common issues during the harmonization and analysis of HLS data, follow these steps:

Check the QA-band for any flags indicating poor-quality data.
Verify the sensor calibration and registration.
Check the data format and resolution.
Consult the user manual and online resources for troubleshooting tips.

Q: What are some best practices for working with HLS data?

A: Some best practices for working with HLS data include:

Always check the QA-band for any flags indicating poor-quality data.
Verify the sensor calibration and registration.
Use the correct data format and resolution.
Consult the user manual and online resources for best practices.

Q: Where can I find more information about HLS data and its applications?

A: You can find more information about HLS data and its applications on the following websites:

NASA's AppEEARS website (https://appeears.earthdatacloud.nasa.gov/task/area)
The HLS data website (https://landsat.gsfc.nasa.gov/hls/)
The QGIS website (https://www.qgis.org/en/site/)