Package: openet-ptjpl
WARNING: This code is in development, is being provided without support, and is subject to change at any time without notificationThis repository provides an Earth Engine Python API based implementation of the PT-JPL model for computing evapotranspiration (ET).Through ecophysiological constraint functions, PT-JPL retrieves actual ET by reducing potential ET starting with the Priestley-Taylor equation (PriestleyTaylor1972). A series of ecophysiological scalar functions, based on atmospheric vapor pressure deficit, relative humidity, and vegetation indices simultaneously reduce potential ET to actual ET, and partition total ET into three sources for canopy transpiration, soil evaporation, and interception evaporation (Fisher2008). PT-JPL is run globally and continuously in space and time with no need for calibration or site-specific parameters.Model DesignThe primary component of the PT-JPL model is the Image() class.  The Image class can be used to compute a single ET image from a single input image.  The Image class should generally be instantiated from an Earth Engine Landsat image using the collection specific methods listed below.  ET image collections can be built by computing ET in a function that is mapped over a collection of input images.  Please see theExample Notebooksfor more details.Input CollectionsPT-JPL can currently be computed for Landsat Collection 2 Level 2 (SR/ST) images  images from the following Earth Engine image collections:LANDSAT/LT05/C02/T1_L2LANDSAT/LE07/C02/T1_L2LANDSAT/LC08/C02/T1_L2LANDSAT/LC09/C02/T1_L2Landsat Collection 2 SR/ST Input ImageTo instantiate the class for a Landsat Collection 2 SR/ST image, use the Image.from_landsat_c2_sr method.The input Landsat image must have the following bands and properties:SPACECRAFT_IDBand NamesLANDSAT_5SR_B1, SR_B2, SR_B3, SR_B4, SR_B5, SR_B7, ST_B6, QA_PIXELLANDSAT_7SR_B1, SR_B2, SR_B3, SR_B4, SR_B5, SR_B7, ST_B6, QA_PIXELLANDSAT_8SR_B1, SR_B2, SR_B3, SR_B4, SR_B5, SR_B6, SR_B7, ST_B10, QA_PIXELLANDSAT_9SR_B1, SR_B2, SR_B3, SR_B4, SR_B5, SR_B6, SR_B7, ST_B10, QA_PIXELPropertyDescriptionsystem:indexLandsat Scene IDMust be in the Earth Engine format (e.g. LC08_044033_20170716)Used to lookup the scene specific c-factorsystem:time_startImage datetime in milliseconds since 1970SPACECRAFT_IDUsed to determine which Landsat typeMust be: LANDSAT_5, LANDSAT_7, LANDSAT_8, or LANDSAT_9Model OutputThe primary output of the PT-JPL model is the actual ET (ETa) in millimeters.Exampleimportopenet.ptjplasptjpllandsat_img=ee.Image('LANDSAT/LC08/C02/T1_L2/LC08_044033_20170716')et_actual=ptjpl.Image.from_landsat_c2_sr(landsat_img).etExample NotebooksMeteorologyTheGEE NLDAS hourly image collectionis the default and only currently supported meteorology source for the hourly air temperature, vapor pressure, windspeed, and incoming short and longwave solar radiation.Ancillary DatasetsOptimal temperature (Topt)Maximum fraction of absorbed photosynthetically active radiation (fAPARmax)InstallationThe OpenET PT-JPL python module can be installed via pip:pip install openet-ptjplDependenciesearthengine-apiopenet-coreOpenET Namespace PackageEach OpenET model is stored in the “openet” folder (namespace).  The model can then be imported as a “dot” submodule of the main openet module.import openet.ptjpl as modelDevelopment and TestingPlease see theCONTRIBUTING.rst.References[Fisher2008]Fisher, J., K. Tu, and D. Baldocchi (2008). Global estimates of the land-atmosphere water flux based on monthly AVHRR and ISLSCP-II data, validated at 16 FLUXNET sites,Remote Sensing of Environment, 112(3), 901-919.https://doi.org/10.1016/j.rse.2007.06.025[PriestleyTaylor1972]Priestley, C. and R. Taylor (1972). On the assessment of surface heat flux and evaporation using large scale parameters.Monthly Weather Review, 100, 81–92.https://doi.org/10.1175/1520-0493%281972%29100%3C0081%3AOTAOSH%3E2.3.CO%3B2