# OpenET Collection v2.0 Pre-2000 (1985-1999) Monthly Image Archive

Archive/backup copies of the OpenET monthly image assets available in the OpenET Publisher Data Catalog Google Earth Engine.


## Model Evapotranspiration (ET)

Monthly images of actual ET are available for five OpenET models: EEMETRIC, GEESEBAL, PTJPL, SIMS, and SSEBop

### Spatial/Temporal Coverage

#### CONUS/GRIDMET

Monthly ET images in the "conus/gridmet" folders were generated using bias corrected GRIDMET reference ET data (see "Reference ET" below) for interpolating from the Landsat overpass scenes to the monthly total.  Images are only available for the western and central United States, covering UTM zones 10-15.  True full CONUS coverage is available in OpenET Collection v2.1.

Start Date: 
: 2001-01-01

End Date
: 2024-12-31

### MGRS Grid Zone Tiling

OpenET monthly ET images are built and stored as tiles based on the MGRS grid zone designation system (https://mgrs-data.org/about/) in order to minimize reprojection of the source Landsat images.  The MGRS grid zones are separated by UTM zone and 6 degree latitude bands.  

Each MGRS grid zone tile will use the spatial reference of the corresponding UTM zone.  For example, all MGRS grid zone "11T" images use the "WGS84 UTM zone 11N" (EPSG:32611) projection.

### Variables

| Band name | Units           | Description |
| --------- | -----           | ----------- |
| et        | millimeter [mm] | Actual evapotranspiration computed by the OpenET models |
| count     | unitless        | Number of clear Landsat observations during the image month that were used in the interpolation process to compute the monthly ET value |

### Model Versions

| Model Name | Version |
| ---------- | ------- |
| EEMETRIC   | 0.20.26 |
| GEESEBAL   | 0.2.2   |
| PTJPL      | 0.2.1   |
| SIMS       | 0.1.1   |
| SSEBop     | 0.2.6/0.2.8* |

*SSEBop model versions are functionally identical, but a change was made part way through processing to reduce memory usage during interpolation step.

### Google Earth Engine (GEE) Image Collections

Images were exported from the image collections in the GEE OpenET Publisher Data Catalog. 

https://developers.google.com/earth-engine/datasets/catalog/projects_openet_assets_eemetric_conus_gridmet_monthly_v2_0_pre2000
https://developers.google.com/earth-engine/datasets/catalog/projects_openet_assets_geesebal_conus_gridmet_monthly_v2_0_pre2000
https://developers.google.com/earth-engine/datasets/catalog/projects_openet_assets_ptjpl_conus_gridmet_monthly_v2_0_pre2000
https://developers.google.com/earth-engine/datasets/catalog/projects_openet_assets_sims_conus_gridmet_monthly_v2_0_pre2000
https://developers.google.com/earth-engine/datasets/catalog/projects_openet_assets_ssebop_conus_gridmet_monthly_v2_0_pre2000



## Ensemble ET

OpenET monthly ensemble assets are computed from the six monthly model ET values.

The ensemble ET is computed as the mean of the ensemble after filtering outliers using the median absolute deviation (MAD) and retaining a minimum of four individual ensemble members.

### Spatial/Temporal Coverage

#### CONUS/GRIDMET

Monthly ET images in the "conus/gridmet" folders were generated using bias corrected GRIDMET reference ET data (see below).  Images are only available for the western and central United States, covering UTM zones 10-15.  

Start Date
: 1985-01-01

End Date
: 1999-09-30

### Variables

| Band name   | Units           | Description |
| ---------   | -----           | ----------- |
| et          | millimeter [mm] | Monthly ensemble actual evapotranspiration (ET) |
| model_count | unitless        | Number of models used to compute the ensemble ET value |
| model_index | unitless        | Bitmask indicating which models were included in the ensemble ET value, after filtering for outliers using the median absolution deviation (mad) |

### Google Earth Engine (GEE) Image Collections

Images were exported from the image collections in the GEE OpenET Publisher Data Catalog. 

https://developers.google.com/earth-engine/datasets/catalog/projects_openet_assets_ensemble_conus_gridmet_monthly_v2_0_pre2000



## Reference ET

### CONUS/GRIDMET

Bias corrected GRIDMET reference ET for the CONUS.

https://doi.org/10.5281/zenodo.18807224

https://www.climatologylab.org/gridmet.html

Start Date
: 1980-01-01

End Date
: 2024-12-31

### Variables

| Band name             | Units           | Description          |
| ---------             | -----           | -----------          |
| eto                   | millimeter [mm] | Grass reference ET   |
| etr                   | millimeter [mm] | Alfalfa reference ET |



## Data License

CC-BY-4.0