Reference Evapotranspiration (ET) Tool Version 1.0 Author: Heather Dinon

This reference ET tool uses Google Map technology to display the data in two different ways-- in a map-based format or as a time series plot. The map-based product is a daily reference ET estimate based on the Penman-Monteith equation in the UN Food and Agriculture Organization paper number 56 (FAO56), and allows the user to select a date from January 1, 2002 to yesterday. From the dynamic map product, users can display an annual time series for a particular station.

For more detailed information on the FAO56 Penman-Monteith method, please refer to the UN FAO56 Penman-Monteith documentation: http://www.fao.org/docrep/X0490E/X0490E00.htm

Usage

git clone git://github.com/open-agroclimate/php-refet.git
cd php-refet
git submodule init
git submodule update

Known Limitations/Caveats

1. Due to a limitation with the CRONOS API (currently being fixed), the six daily meteorological input parameters for the reference ET estimate (min/max temperature, min/max relative humidity, average wind speed, and average solar radiation) will be computed from hourly data even if <80% of the hourly data is available to compute these daily values. This could lead to bad values being output from the reference ET calculation.

2. User needs to obtain an API key from Google for their server or local machine. Sign up for this here: http://code.google.com/apis/maps/signup.html

3. Users may need to limit chart code to pull only about 3 years of data so that page load speed is <5secs.

4. Users may have to change location of their cronos.php file (in require_once())