An evaporation sensor measures the rate of water evaporation from a surface, which is a critical parameter in hydrological, meteorological, and agricultural studies. Understanding evaporation rates helps in water resource management, irrigation planning, and climate modeling.

Working Principle

The working principle of an evaporation sensor revolves around the measurement of water loss over time from a standardized open pan or a more sophisticated instrument setup designed to mimic natural conditions. Here are the two primary types of setups used in evaporation measurement:

1. Class A Evaporation Pan:
   • This is the traditional method using a standardized circular pan made of galvanized iron or another suitable material with a specific diameter and depth.
   • The pan is filled with water, and the water level is measured at regular intervals using a fixed point or a hook gauge to determine the amount of water evaporated over a given period.
   • Environmental factors like temperature, humidity, wind speed, and solar radiation directly influence the rate of evaporation measured by the pan.
2. Electronic Evaporation Sensors:
   • These are modern instruments equipped with sensors to measure the parameters affecting evaporation directly and calculate the evaporation rate electronically.
   • They often include a water temperature sensor, air temperature and humidity sensors, and a wind sensor to dynamically measure conditions affecting evaporation rates.
   • Some electronic sensors use a lysimeter setup where the loss of water from a column of soil is measured, which can be more representative of actual ground conditions.

Standards

Evaporation sensors, especially evaporation pans, are standardized to ensure consistency and comparability of data across different locations and timeframes. The most common standards associated with evaporation sensors include:

• World Meteorological Organization (WMO):
  • Provides guidelines on the installation, use, and maintenance of evaporation measuring instruments.
  • The Class A pan, as specified by the WMO, is one of the global standards for evaporation measurement, with specific dimensions (usually about 120 cm in diameter and 25 cm in depth).
• American Society of Civil Engineers (ASCE):
  • The ASCE has guidelines for the measurement of evaporation using more sophisticated instrumentation and methods, which may include automated sensors and adjusted setups to more closely mimic natural environmental conditions.
• ISO Standards:
  • There are also international standards under the ISO that define the characteristics of the materials used in evaporation sensors, their calibration processes, and data interpretation methods.

Using these standards helps ensure that evaporation data are reliable and can be used in scientific and practical applications to make informed decisions about water management. The choice between traditional pan methods and electronic sensors often depends on the required accuracy, the environmental conditions, and the availability of resources to maintain and monitor the equipment.