Key Takeaways
- NDVI data can be obtained from various government agencies like USGS and NOAA.
- Sources like USGS Landsat and MODIS provide free NDVI data derived from satellite imagery.
- Daily, global NDVI data is available spanning multiple decades from NOAA CDR and AVHRR datasets.
- Higher resolution commercial satellites from Planet Labs and others also provide NDVI data for purchase.
- Google Earth Engine allows users to generate customized NDVI layers by uploading or processing satellite data.
- Understanding the source, resolution, and time period of NDVI data is key for appropriate application.
Introduction
Normalized Difference Vegetation Index (NDVI) data provides valuable information about the density and health of vegetation based on how it reflects light at different wavelengths. But where can one find and access NDVI datasets for use in research, agriculture, forestry, and other applications? This comprehensive guide will evaluate the major sources to acquire free and paid NDVI data products, from coarse global datasets to high resolution commercial satellite imagery. It will outline the key features, options, and considerations in obtaining NDVI data from government agencies, online platforms, and commercial providers. Discover the range of available NDVI data to meet diverse analytical needs.
NDVI data serves as an important tool for monitoring and analyzing vegetation at different scales. This guide will empower readers to find the most appropriate NDVI data source and product for their purpose. Whether you need global, regional, or local NDVI data for a specific time period, this article explores the various options available. Read on to determine the best NDVI data source based on your requirements and resources.
What are the major free and open sources for NDVI data?
Government agencies such as United States Geological Survey (USGS) and National Oceanic and Atmospheric Administration (NOAA) provide free and publicly accessible NDVI data products derived from satellite sensors. These sources offer NDVI data with varying spatial, temporal, and spectral characteristics.
USGS Landsat NDVI
One of the most widely used free sources of satellite-based NDVI data is the USGS Landsat NDVI portal. It provides global coverage of NDVI layers calculated from Landsat satellite imagery at 30 meter resolution. The available NDVI composite images are already preprocessed and can be easily added to GIS software for vegetation monitoring and analysis.
Landsat NDVI data enables local, regional, and global scale vegetation studies and covers a long timeframe from 1999 to present. However, the 16-day revisit period of Landsat limits the ability to capture rapid vegetation changes. Landsat NDVI data works well for general landscape monitoring rather than detailed crop-specific analysis.
USGS EROS Archive – NOAA CDR NDVI
For higher temporal resolution NDVI data, the USGS EROS Archive provides daily global NDVI images since 1981 based on NOAA’s Advanced Very High Resolution Radiometer (AVHRR) sensor at 4 km resolution. This NOAA Climate Data Record (CDR) NDVI dataset enables continuous large-area vegetation monitoring and can assess short-term vegetation changes.
The EROS Archive also offers NDVI products from MODIS and VIIRS satellites. However, the NOAA AVHRR NDVI CDR provides the longest consistent, calibrated remote sensing record currently available to researchers and analysts. The data is provided in network Common Data Form (netCDF) format.
MODIS NDVI
Moderate Resolution Imaging Spectroradiometer (MODIS) sensors on NASA’s Terra and Aqua satellites provide NDVI data at 250 meter resolution. The MODIS Vegetation Index products are derived from daily surface reflectance and available from 2000 to present. The 16-day composite NDVI minimizes cloud cover and other contamination effects.
MODIS NDVI provides consistent, continuous measurements over large areas making it suitable for regional scale vegetation monitoring and time series analysis. It is also available in gridded formats for easier usage. However, the coarse resolution may limit applicability for detailed vegetation studies at farm or field scales.
What commercial remote sensing platforms provide NDVI data?
Several satellite companies now provide on-demand NDVI data at very high resolutions, but this data comes at a cost. Commercial options to consider include:
Planet Labs
Founded in 2010, Planet Labs operates over 200 Earth observation satellites, the largest private satellite fleet. Their PlanetScope and SkySat satellites collect high resolution NDVI data (3-5 meters) in variousAnalysis Ready Data packages. NDVI layers can be customized based on user needs.
Planet Labs data services enable detailed crop monitoring, forest canopy analysis, and other precision agriculture and environmental applications. However, purchasing the imagery can be costly depending on area and revisit period required.
Maxar Technologies
Maxar’s constellation provides very high resolution NDVI data (30-50 cm) from sensors like GeoEye-1, WorldView-2 and WorldView-3. These satellites have dedicated NDVI bands and strict radiometric calibration to enable accurate quantitative vegetation analysis.
Maxar offers subscription-based NDVI imagery services which can be ingested into a variety of agriculture field management and analytics software platforms. The extremely high resolution enables field-level insights.
Hexagon / Deimos Imaging
Through its Deimos Imaging program, Hexagon provides fused radar and multispectral satellite imagery to generate very high resolution NDVI layers. By combining optical and radar data, their NDVI layers provide more frequent revisits and reduced cloud contamination effects.Targeted towards precision agriculture, their NDVI services enable monitoring crop growth and conditions during a growing season.
How can I generate custom NDVI data using Google Earth Engine?
Google Earth Engine (GEE) provides a powerful cloud platform to process and analyze geospatial data using Google’s computing capabilities. GEE hosts a massive catalog of earth observation data and enables users to create custom NDVI layers from raw satellite imagery.
Using JavaScript or Python APIs, users can upload their own multispectral satellite data to GEE, apply preprocessing, calculate NDVI, and export the output. GEE also contains scripts to process NDVI from public satellite data like Landsat, Sentinel and MODIS. This allows generating NDVI layers for specific regions and time periods tailored to project needs.
GEE provides great flexibility but requires coding skills and understanding of image processing workflows. Expertise is needed to handle issues like cloud contamination or noisy data. GEE is ideal for generating customized NDVI for research applications rather than operational monitoring. Limits on processing power may apply for large study areas or frequent computations.
What factors should I consider when selecting an NDVI data source?
When evaluating NDVI data sources, key aspects to consider are:
- Spatial resolution: Higher resolution enables studying vegetation at finer scales but can be more expensive. Resolutions below 10 meters may be needed for field-level crop analysis. Global datasets tend to be 250-500 meters.
- Temporal resolution: Frequent revisits are needed to capture rapid vegetation changes. Daily revisits are possible with some satellite constellations and gridded products. Higher latency in data availability may be a tradeoff.
- Time period covered: Long-term consistent datasets like NOAA AVHRR enable historical trend analysis. Newer sensors provide better quality data.
- Cloud contamination: Compositing and smoothing techniques help overcome cloud cover but may reduce data quality.
- Radiometric calibration: Well calibrated data allows quantitative comparison between dates.
- Data formats and processing: Options include analysis-ready data formats or raw data requiring preprocessing expertise.
- Costs: Purchasing commercial high resolution imagery substantially increases costs compared to free government data.
- Licensing: Public domain data has no usage restrictions while commercial data may limit sharing or redistribution.
How can I access, process, and analyze NDVI data?
Once relevant NDVI data is identified, users need tools and expertise to access, process, and analyze it effectively:
- File formats like GeoTIFF, netCDF or text-based formats are commonly used to share and access NDVI data. GIS software like QGIS provides NDVI data visualization, processing and basic analysis capabilities.
- Pixel-based analytics to generate NDVI outputs for defined areas can be done in Python using libraries like NumPy, SciPy, Pandas. The R programming language also provides tools for statistical analysis of NDVI data.
- Platforms like Google Earth Engine allow sophisticated analysis of NDVI without needing to download and process large datasets locally. JavaScript and Python APIs help run customized analytic workflows on cloud infrastructure.
- Machine learning algorithms can help detect changes in vegetation patterns and correlate NDVI with various predictive factors. Tools like TensorFlow, PyTorch and scikit-learn enable advanced NDVI analytics.
- Time series NDVI data can provide insights into phenological cycles. Techniques like smoothing, interpolation, decomposition and outlier detection help model vegetation temporal signatures.
- Proper interpretation of NDVI data requires understanding vegetation characteristics, data uncertainties, and potential processing artifacts. Combining NDVI with other data provides more robust insights.
Conclusion
A variety of free and commercial NDVI datasets exist to meet diverse user needs and applications ranging from global monitoring to targeted crop analysis. Key government sources include Landsat, MODIS and NOAA AVHRR providing different balances of coverage, resolution and time period. Commercial satellites can provide very high resolution NDVI data on-demand. Google Earth Engine enables customized generation of NDVI layers using public and user data.
Carefully evaluating spatial, temporal, spectral and cost factors is necessary to select the optimal NDVI source for a particular use case. Powerful analytic platforms provide capabilities to process, model and interpret NDVI data to derive actionable vegetation intelligence. Properly applying NDVI data along with ground-truthing and validation enables gaining unique insights into vegetation health, density and conditions
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