Penman-Monteith-Leuning model (abbreviated as PML_V1
) was proposed by Leuning
et al. (2008), and further improved by Zhang et al., (2010, 2016). In PML,
evaporation is divided into: transpiration from vegetation (Ec), direct
evaporation from the soil (Es) and vaporization of intercepted rainfall from
vegetation (Ei).
PML_V2
was developed by Gan et al., (2018) and Zhang et al., (2019), which coupled ET and gross primary
products via canopy conductance theory. They are both in the resolution of 500 m
and 8-day, and range from -60°S to 90°N.
Figure 1. Flowchart of global forcing data processing and PML_V2
modeling processes.
Variable | Description | Unit |
---|---|---|
Tmax | daily maximum temperature | °C |
Tmin | daily minimum temperature | °C |
Tavg | daily mean temperature | °C |
Pa | atmosphere pressure | kPa |
U | wind speed at 10-m height | m/s |
q | specific humidity | kg/kg |
Prcp | precipitation | mm/d |
Rln | inward longwave solar radiation | W/m2 |
Rs | inward shortwave solar radiation | W/m2 |
Pi | the difference of Prcp and Ei | mm/d |
Es_eq | equilibrium evaporation | mm/d |
ET_water | evaporation from water body, snow and ice | mm/d |
qc | quality control variable for albedo and surface emissivity. | - |
Table 1. PML_V1
and PML_V2
bands information (PML_V1
have no GPP band, other
bands are some).
Note: Only PMLV1 is available currently.
BandName | Units | Scale | Description |
---|---|---|---|
GPP | gC m-2 d-1 | 0.01 | Gross primary product |
Ec | mm d-1 | 0.01 | Vegetation transpiration |
Es | mm d-1 | 0.01 | Soil evaporation |
Ei | mm d-1 | 0.01 | Interception from vegetation canopy |
ET_water | mm d-1 | 0.01 | Water body, snow and ice evaporation. Penman evapotranspiration is regarded as actual evaporation for them. |
qc | - | - | Interpolation information for Albedo and Emissivity. Bitmask for qc: Bits 0-2: Emissivity interpolation information 0: good value, no interpolation 1: linear interpolation 2: history 8-day average interpolation 3: history monthly average interpolation Bits 3-5: Albedo interpolation information Same as Emissivity. |
Click the following links to get the access. The corresponding links are:
- PML_V1 https://code.earthengine.google.com/?asset=projects/pml_evapotranspiration/PML/OUTPUT/PML_V1_8day
- PML_V2 https://code.earthengine.google.com/?asset=projects/pml_evapotranspiration/PML/OUTPUT/PML_V2_8day_v014
PML products are standard ee.ImageCollection
object in GEE.
You can clip regional data by polygon shapefile from ee.ImageCollection
.
- Upload your polygon shapefile to GEE https://developers.google.com/earth-engine/importing
- Download data from GEE
https://developers.google.com/earth-engine/exporting
- For small regions, you can transform
ee.ImageCollection
into multiple bandsee.Image
. In this way, you can download all the dataset in a time: - For large regions, you have to download trough
ee.ImageCollection
.
Clip and export the regional data you need by the polygon shapefile you uploaded. This is a little example.
[1]. Zhang, Y., Kong, D., Gan, R., Chiew, F.H.S., McVicar, T.R., Zhang, Q., and Yang, Y.. (2019) Coupled estimation of 500m and 8-day resolution global evapotranspiration and gross primary production in 2002-2017. Remote Sens. Environ. 222, 165-182, https://doi:10.1016/j.rse.2018.12.031
[2]. Zhang, Y., Peña-Arancibia, J.L., McVicar, T.R., Chiew, F.H.S., Vaze, J., Liu, C., Lu, X., Zheng, H., Wang, Y., Liu, Y.Y., Miralles, D.G., Pan, M., 2016. Multi-decadal trends in global terrestrial evapotranspiration and its components. Sci. Rep. 6, 19124. https://doi.org/10.1038/srep19124
[3]. Zhang, Y., Leuning, R., Hutley, L.B., Beringer, J., McHugh, I., Walker, J.P., Using long-term water balances to parameterize surface conductances and calculate evaporation at 0.05°spatial resolution. Water Resour. Res. 46. https://doi.org/10.1029/2009WR008716
[4]. Leuning, R., Zhang, Y.Q., Rajaud, A., Cleugh, H., Tu, K., 2008. A simple surface conductance model to estimate regional evaporation using MODIS leaf area index and the Penman- Monteith equation. Water Resour. Res. 44. https://doi.org/10.1029/2007WR006562
[5]. Gan, R., Zhang, Y., Shi, H., Yang, Y., Eamus, D., Cheng, L., Chiew, F.H.S., Yu, Q., 2018. Use of satellite leaf area index estimating evapotranspiration and gross assimilation for Australian ecosystems. Ecohydrology. e1974. https://doi.org/10.1002/eco.1974
[6]. Gorelick, N., Hancher, M., Dixon, M., Ilyushchenko, S., Thau, D., Moore, R., 2017. Google Earth Engine: Planetary-scale geospatial analysis for everyone. Remote Sens. Environ. 202, 18–27. https://doi.org/10.1016/j.rse.2017.06.031