Evapotranspiration forecasting irrigation control system

• US 5,696,671 A
• Filed: 01/06/1997
• Issued: 12/09/1997
• Est. Priority Date: 02/17/1994
• Status: Expired due to Term

• Current Assignee: Waterlink Systems Incorporated
• Original Assignee: Waterlink Systems Incorporated
• Inventors: Oliver, Michael James
• Primary Examiner(s): RUGGIERO, JOSEPH F
• Application Number:
  US08/779,337
• Time in Patent Office: 337 Days
• Field of Search: 364/140-147, 364/420, 364/509, 364/510, 137/624.11, 137/624.2, 239/63, 239/69, 239/70, 395/928, 395/930, 395/931
• US Class Current: 700/284
• CPC Class Codes: A01G 25/16 Control of watering
• CPC Class Codes: A01G 25/167 Control by humidity of the soil itself or of devices simulating soil or of the atmosphere; Soil humidity sensors
• CPC Class Codes: Y02A 40/10 in agriculture
• CPC Class Codes: Y02A 40/22 Improving land use; Improving water use or availability; Controlling erosion

Abstract

A method and apparatus for using predictive evapotranspiration (ET) and precipitation data in controlling automated and semi-automated irrigation systems. In accordance with the present invention, the conventional use of ET values is modified to take into account predicted or forecast weather events. By using forecast weather data in computing ET values, a substantial savings in water use can be achieved. Past or historical meteorological data is used to make corrective adjustments to the watering schedules that have been predicted using meteorological forecasting. That is, as each day becomes past or historical, adjustments to the overall cumulative depletion of water in the soil need to be made. When an irrigation site is to be updated with a new watering schedule, actual meteorological data is first used to correct any differences between the previously forecast and actual meteorological data to the current day. After past cumulative depletion has been determined, future predictions of precipitation and ET values are used to determine when and how much to water. Future meteorological data predictions can be updated or modified as new data becomes available, thereby allowing closer matching of predicted ET values with actual ET values. Modifying meteorological data on a daily basis results in predictions that more closely follow actual ET values than updating on a weekly or longer schedule.

Claims

1. A method for efficiently controlling irrigation, including the steps of:

(a) determining evapotranspiration data characteristics of an irrigation site;

(b) determining forecast meteorological data, including expected precipitation, for the irrigation site based on current meteorological conditions;

(c) forecasting an ETo value, ETo'"'"', from the forecast meteorological data;

(d) calculating a current soil moisture depletion value Cd_t for the irrigation site as proportional to a previous soil moisture depletion value Cd_t-1 for the irrigation site plus a daily depletion value Dd that depends upon the evapotranspiration data characteristics of the irrigation site, less an effective expected precipitation value, Peff, determined from the forecast meteorological data;

(e) electronically computing a watering schedule based upon at least the current soil moisture depletion value Cd_t ; and

(f) applying the computed watering schedule to at least one irrigation control system to control at least one irrigation valve of such control system in accordance with such watering schedule, wherein the computed watering schedule controls when and how much to irrigate through each irrigation valve.

2. The method of claim 1, further including the steps of:

(a) computing the watering schedule remotely from the irrigation control system;

(b) communicating the watering schedule to the irrigation control system.

3. A system for efficiently controlling irrigation, including:

(a) means for receiving evapotranspiration data characteristics of an irrigation site;

(b) means for receiving forecast meteorological data, including expected precipitation, for the irrigation site based on current meteorological conditions;

(c) means for forecasting an ETo value, ETo'"'"', from the forecast meteorological data;

(d) means for calculating a current soil moisture depletion value Cd_t for the irrigation site as proportional to a previous soil moisture depletion value Cd_t-1 for the irrigation site plus a daily depletion value Dd that depends upon the evapotranspiration data characteristics of the irrigation site, less an effective expected precipitation value, Peff, determined from the forecast meteorological data;

(e) means for electronically computing a watering schedule based upon at least the current soil moisture depletion value Cd_t ; and

(f) communication means for applying the computed schedule to at least one irrigation control system to control at least one irrigation valve coupled to such control system in accordance with such schedule, wherein the computed schedule controls when and how much to irrigate through each irrigation valve.

4. The system of claim 3, wherein:

(a) the means for electronically computing a watering schedule computes a watering schedule remotely from the irrigation control system;

(b) the means for electronically computing a watering schedule further includes means for coupling to a communications system for communicating the watering schedule to the irrigation control system.

5. A system for efficiently controlling irrigation, including:

(a) at least one irrigation control system coupled to at least one irrigation valve;

(a) means for receiving evapotranspiration data characteristics of an irrigation site;

(b) means for receiving forecast meteorological data, including expected precipitation, for the irrigation site based on current meteorological conditions;

(c) means for forecasting an ETo value, ETo'"'"', from the forecast meteorological data;

(d) means for calculating a current soil moisture depletion value Cd_t for the irrigation site as proportional to a previous soil moisture depletion value Cd_t-1 for the irrigation site plus a daily depletion value Dd that depends upon the evapotranspiration data characteristics of the irrigation site, less an effective expected precipitation value, Peff, determined from the forecast meteorological data;

(e) means for electronically computing a watering schedule based upon at least the current soil moisture depletion value Cd_t ; and

(c) communication means for applying the computed schedule to at least one irrigation control system to control at least one irrigation valve in accordance with such schedule, wherein the computed schedule controls when and how much to irrigate through each irrigation valve.

6. The system of claim 5, wherein:

(a) the means for electronically computing a watering schedule computes a watering schedule remotely from the irrigation control system;

(b) the means for electronically computing a watering schedule further includes means for coupling to a communications system for communicating the watering schedule to the irrigation control system.

7. A computer program, residing on a computer-readable medium, for efficiently controlling an irrigation system, the computer program comprising instructions for causing a computer to:

(a) receive evapotranspiration data characteristics of an irrigation site

(b) receive forecast meteorological data, including expected precipitation, for the irrigation site based on current meteorological conditions;

(c) forecast an ETo value, ETo'"'"', from the forecast meteorological data;

(d) calculate a current soil moisture depletion value Cd_t for the irrigation site as proportional to a previous soil moisture depletion value Cd_t-1 for the irrigation site plus a daily depletion value Dd that depends upon the evapotranspiration data characteristics of the irrigation site, less an effective expected precipitation value, Peff, determined from the forecast meteorological data;

(e) compute a watering schedule based upon at least the current soil moisture depletion value Cd_t, the computed watering schedule defining when and how much to irrigate through each irrigation valve of at least one irrigation control system.

8. The computer program of claim 7, wherein the computer program further comprises instructions for causing a computer to:

(a) communicate the watering schedule to each irrigation control system from a site remote from each irrigation control system.