1. Analysis Ready Data July 18, 2016 John Dwyer Leo Lymburner
Landsat Project Scientist, USGS
Leo Lymburner
Land Cover Team Lead, GA

2. Why is ARD critical? Advantages for producers Advantages for end users
Facilitates expedient access
More efficient data management
Traceability of data provenance
Enables targetted data retrieval and utilisation – reduction in data transfer volumes
Advantages for end users
Enable automated analysis
Support sensor interoperability
Less effort on preprocessing – more time to generate higher level products

3. In simplest terms analysis ready data should be…
Measurements of the Earths surface
from the same sensor and the same
wavelength are comparable in space
and time
…and preferably…
Measurements from the different sensors and
the same wavelength are comparable in
space and time

4. Geometric alignment Different origins Sensor specific acquisition
orientation
Grids don’t line up

5. Spatial comparability of different collections
Characterise the geometric accuracy of each sensor collection

6. The challenge of different spatial resolutions
Sentinel 2
Landsat
MODIS

7. per pixel metadata Time PQ flagged per band -Saturation
PQ flagged observation
-Cloud

8. Spectral comparability
ARD must allow users
To keep track of the sensor
That acquired a measurement
Sensor 1 ‘Blue Band’
Sensor 2 ‘Blue Band’
Sensor 3 ‘Blue Band’

9. Community Established Terms
NASA EOS Processing Levels
Level-0: Reconstructed, unprocessed instrument and payload data
Level-1: Data that have been processed to sensor units
Level-2: Derived geophysical variables at the same resolution and location as Level 1 source data.
Level-3: Variables mapped on uniform space-time grid scales, usually with some completeness and consistency.
Level-4: Model output or results from analyses of lower-level data (e.g., variables derived from multiple measurements).

10. Hierarchical Definition of ARD
ARD Level
Data Type
Example / Description
NASA EOS
Threshold
Target
Break- through
ARD-Specialist corrections
Scene-based calibrated radiances
Level-1T Scaled DNs
2G/1 X
Scene-based TOA reflectance
Level-1T TOA reflectance
ARD-Specialist analysis
Scene-based surface reflectance
Level-1T atmospherically corrected only
2G/2
Scenes of Nadir view angle corrected BRDF corrected atmospherically corrected surface reflectance
Seamless atmospherically corrected surface reflectance
Gridded surface reflectance with corresponding pixel quality flags (could be from either scene-based SR options above) 3
ARD-utilisation by non-EO community
Surface reflectance composites
Best available pixel composites per epoch (could be from either scene-based SR options above) 4
A comprehensive framework to highlight the risk of people misinterpreting what ARD is/means
Need to narrow the focus to GA/USGS ARD collections
Surface Temperature is next on the list…

11. Hierarchical Definition of ARD
ARD Level
Data Type
Example / Description
NASA EOS
Threshold
Target
Break- through
ARD-Specialist corrections
Scene-based calibrated radiances
Level-1T Scaled DNs
2G/1 X
Scene-based TOA reflectance
Level-1T TOA reflectance
ARD-Specialist analysis
Scene-based surface reflectance
Level-1T atmospherically corrected only
2G/2
Scenes of Nadir view angle corrected BRDF corrected atmospherically corrected surface reflectance
Seamless atmospherically corrected surface reflectance
Gridded surface reflectance with corresponding pixel quality flags (could be from either scene-based SR options above) 3
 TOA SR
 NBAR
ARD-utilisation by non-EO community
Surface reflectance composites
Best available pixel composites per epoch (could be from either scene-based SR options above) 4
A comprehensive framework to highlight the risk of people misinterpreting what ARD is/means
Need to narrow the focus to GA/USGS ARD collections
Surface Temperature is next on the list…

12. Proposed LSI-VC/CEOS definition of ARD
Geophysical measurements that are comparable in space and time with sufficient per-pixel (observation) metadata to enable users to select ‘observations of interest’ as input into their analyses.
Or in USGS/GA terms ‘surface reflectance in conjunction with PQ/QA bands’
NASA-EOS level 2 data with metadata
Collection level (e.g. CPF, GCP specification)
Record level ( e.g. time of acquisition)
Pixel level (e.g. PQ/QA band)
The USGS ARD defintiion needs to updated to include additional QA bits associated with surface reflectance - interpolated aerosols, updated cloud information. John will add this info to the PQ//QA tables later in the deck; will try to get this included by the dry-run, but certainly by LA meeting.