Digital Earth Africa GeoMAD

agriculture cog deafrica disaster response earth observation geospatial natural resource satellite imagery stac sustainability

Description

GeoMAD is the Digital Earth Africa (DE Africa) surface reflectance geomedian and triple Median Absolute Deviation data service. It is a cloud-free composite of satellite data compiled over specific timeframes. The geomedian component combines measurements collected over the specified timeframe to produce one representative, multispectral measurement for every pixel unit of the African continent. The end result is a comprehensive dataset that can be used to generate true-colour images for visual inspection of anthropogenic or natural landmarks. The full spectral dataset can be used to develop more complex algorithms. For each pixel, invalid data is discarded, and remaining observations are mathematically summarised using the geomedian statistic. Flyover coverage provided by collecting data over a period of time also helps scope intermittently cloudy areas. Variations between the geomedian and the individual measurements are captured by the three Median Absolute Deviation (MAD) layers. These are higher-order statistical measurements calculating variation relative to the geomedian. The MAD layers can be used on their own or together with geomedian to gain insights about the land surface, and understand change over time. Calculating GeoMAD over different timeframes and sensors provides a range of insights to the environment. An annual timeframe allows better correction for cloud cover and reduces artifacts for comparison over multiple years. A semiannual timeframe, for example six-month blocks, better captures seasonal variation within one year, but can also be used to compare equivalent periods from different years. Likewise, Landsat sensors allows full utility of the surface reflectance archive dating back to 1984, while more recent Sentinel-2 data provides higher-frequency flyovers and better resolution. The Digital Earth Africa GeoMAD service currently provides annual and six-month semiannual datasets, with separate services for Landsat and Sentinel-2 sensors.

Update Frequency

GeoMADs for Sentinel-2 and Landsat are updated as their respective time periods are available.

License

DE Africa makes this data available under the Creative Commons Attribute 4.0 license https://creativecommons.org/licenses/by/4.0/.

Documentation

https://docs.digitalearthafrica.org/en/latest/data_specs/GeoMAD_specs.html

Managed By

See all datasets managed by Digital Earth Africa.

Contact

helpdesk@digitalearthafrica.org

How to Cite

Digital Earth Africa GeoMAD was accessed on DATE from https://registry.opendata.aws/deafrica-geomad.

Usage Examples

Tutorials
Tools & Applications
Publications

Resources on AWS

  • Description
    Sentinel-2 GeoMAD (Annual) data
    Resource type
    S3 Bucket
    Amazon Resource Name (ARN)
    arn:aws:s3:::deafrica-services/gm_s2_annual
    AWS Region
    af-south-1
    AWS CLI Access (No AWS account required)
    aws s3 ls s3://deafrica-services/gm_s2_annual/ --region af-south-1 --no-sign-request
    Explore
    STAC V1.0.0 endpoint
  • Description
    Sentinel-2 GeoMAD (Semi-Annual) data
    Resource type
    S3 Bucket
    Amazon Resource Name (ARN)
    arn:aws:s3:::deafrica-services/gm_s2_semiannual
    AWS Region
    af-south-1
    AWS CLI Access (No AWS account required)
    aws s3 ls s3://deafrica-services/gm_s2_semiannual/ --region af-south-1 --no-sign-request
    Explore
    STAC V1.0.0 endpoint
  • Description
    Landsat 8 GeoMAD (Annual) data
    Resource type
    S3 Bucket
    Amazon Resource Name (ARN)
    arn:aws:s3:::deafrica-services/gm_ls8_annual
    AWS Region
    af-south-1
    AWS CLI Access (No AWS account required)
    aws s3 ls s3://deafrica-services/gm_ls8_annual/ --region af-south-1 --no-sign-request
    Explore
    STAC V1.0.0 endpoint
  • Description
    Landsat 5 and 7 GeoMAD (Annual) data
    Resource type
    S3 Bucket
    Amazon Resource Name (ARN)
    arn:aws:s3:::deafrica-services/gm_ls5_ls7_annual
    AWS Region
    af-south-1
    AWS CLI Access (No AWS account required)
    aws s3 ls s3://deafrica-services/gm_ls5_ls7_annual/ --region af-south-1 --no-sign-request
    Explore
    STAC V1.0.0 endpoint
  • Description
    S3 Inventory
    Resource type
    S3 Bucket
    Amazon Resource Name (ARN)
    arn:aws:s3:::deafrica-services-inventory
    AWS Region
    af-south-1
    AWS CLI Access (No AWS account required)
    aws s3 ls s3://deafrica-services-inventory/ --region af-south-1 --no-sign-request
  • Description
    Bucket creation event notification, can subscribe with Lambda or SQS. Message sent by deafrica-services bucket contain all object create events.
    Resource type
    SNS Topic
    Amazon Resource Name (ARN)
    arn:aws:sns:af-south-1:543785577597:deafrica-services-topic
    AWS Region
    af-south-1

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