Algorithm Theoretical Basis Document (ATBD)
The MYD16A3 Version 6 Evapotranspiration/Latent Heat Flux product is a yearly composite dataset produced at 500 meter (m) pixel resolution. The improved algorithm is based on the logic of the Penman-Monteith equation, which includes inputs of daily meteorological reanalysis data along with Moderate Resolution Imaging Spectroradiometer (MODIS) remotely sensed data products such as vegetation property dynamics, albedo, and land cover.
Provided in the MYD16A3 product are layers for yearly Evapotranspiration (ET), Latent Heat Flux (LE), Potential ET (PET) and Potential LE (PLE) along with a quality control layer. Two low resolution browse images, ET and LE, are also available for each MYD16A3 granule.
The pixel values for the two Evapotranspiration layers (ET and PET) are the sum for all days within the defined year, and the pixel values for the two Latent Heat layers (LE and PLE) are the average of all days within the defined year.
Validation at stage 3 has been achieved for the MODIS Evapotranspiration data products. Further details regarding MODIS land product validation for the MYD16 data products are available from the MODIS Land Team Validation site.
|File Size||~10 MB|
|Temporal Extent||2002-07-04 to 2003-12-31|
|Geographic Dimensions||1200 km x 1200 km|
|Number of Science Dataset (SDS) Layers||5|
|Columns/Rows||2400 x 2400|
|Pixel Size||500 m|
|SDS Name||Description||Units||Data Type||Fill Value||No Data Value||Valid Range||Scale Factor|
|ET_500m||Total Evapotranspiration||kg/m²/year||16-bit unsigned integer||65529 to 65535||N/A||0 to 65500||0.1|
|LE_500m||Average Latent Heat Flux||J/m²/day||16-bit signed integer||32761 to 32767||N/A||0 to 32700||10000|
|PET_500m||Total Potential Evapotranspiration||kg/m²/year||16-bit unsigned integer||65529 to 65535||N/A||0 to 65500||0.1|
|PLE_500m||Average Potential Latent Heat Flux||J/m²/day||16-bit signed integer||32761 to 32767||N/A||0 to 32700||10000|
|ET_QC_500m||Evapotranspiration Quality Assessment||Percent||8-bit unsigned integer||255||N/A||0 to 100||N/A|
The header file of MYD16A3 lists only one fill value per layer, but there are a total of seven fill values to describe non-vegetated pixels.
|65529||Land cover assigned as "unclassified" or not able to determine|
|65530||Land cover assigned as urban/built-up|
|65531||Land cover assigned as "permanent" wetlands/inundated marshland|
|65532||Land cover assigned as perennial snow, ice|
|65533||Land cover assigned as barren, sparse vegetation (rock, tundra, desert)|
|65534||Land cover assigned as perennial salt or water bodies|
|32761||Land cover assigned as "unclassified" or not able to determine|
|32762||Land cover assigned as urban/built-up|
|32763||Land cover assigned as "permanent" wetlands / inundated marshland|
|32764||Land cover assigned as perennial snow, ice|
|32765||Land cover assigned as barren, sparse vegetation (rock, tundra, desert)|
|32766||Land cover assigned as perennial salt or water bodies|
Quality for MYD16A3 is expressed as a percentage in the ET_QC_500m science dataset layer. More information on how this value is derived can be found in Section 6.2.2 of the User Guide.
Operational and uncertainty issues are provided under Section 3 in the User Guide.