Evapotranspiration

ATMOS 51
VBR Actual ET

Directly measure water loss from the surfaces of your plants and soils to ensure accurate irrigation regardless of growth stage, canopy closure, or plant water status.

Direct measurement of actual ET at field-scale
Uses variance Bowen ratio (VBR) to measure fluxes using a combination of high-frequency temperature, specific humidity, and solar radiation
Simple plug-and-play setup with METER data loggers for remote near-real-time data access

Don’t estimate ET. Measure it.

Knowing exactly how much water a canopy loses during the day is vital to many applications. From irrigation planning to quantifying hydrological changes over time to modeling an ecosystem’s energy balance, direct measurements of evapotranspiration can give you the information you need to make the right decisions at the right time.

The ATMOS 51 VBR Actual ET Sensor takes your data beyond reference evapotranspiration values, using a variance Bowen ratio technique to simplify water and energy balance measurements in the field. Now, you can use actual ET data to accurately measure plant water use throughout the day, identify water limitations, and detect plant stress signals earlier.

Scale measurements to your application

Like conventional field-scale water flux measurements, such as eddy covariance towers, the ATMOS 51 abides by turbulent transport principles to measure energy and water exchange via dynamic eddies. This compact unit measures the same area at a fraction of the cost and with less infrastructure, so you can optimize ET measurements to your application without breaking your budget.

Use the ATMOS 51 to supplement or expand ET measurements throughout your eddy covariance tower footprint or validate crop ET (reference ET) by pairing it with the all-in-one weather stations in your field.

More precision for better decisions

Going beyond reference ET and crop ET means you know exactly how much water is leaving the system. Characterize plant hydraulic stress, optimize irrigation, steer crops, and monitor water conservation efforts with accurate measurements from your site (learn more).

Combine actual ET with precipitation and soil moisture measurements to get a clear, mechanistic understanding of water movement into and out of a system.

Simple setup and data management

The ATMOS 51 uses the same compact design as our other popular ATMOS devices. Setup is as simple as mounting the sensor to an instrument mast and plugging it into a ZL6 data logger. Go from setup to streaming data in as little as 20 minutes.

Feature summary

Actual ET measurements direct from your project site
High frequency temperature, specific humidity, and solar radiation extend data
Plug-and-play compatibility with ZL6 data loggers and ZENTRA Cloud
Easy installation with the built-in leveling bracket
Reduced maintenance needs due to the UV-resistant plastic housing

Measurement Specifications

Solar Radiation
Range: 0–1750 W/m²
Resolution: 1 W/m²
Accuracy: ±5% of measurement typical

Relative Humidity (RH)
Range: 0–100% RH (0.00–1.00)
Resolution: ±0.01% RH
Accuracy: ±1% RH, typical
Long-term drift: ±0.25% of RH/year, typical

Humidity Sensor Temperature
Range: –40 to 60 °C
Resolution: 0.01 °C
Accuracy: ±0.1 °C

Barometric Pressure
Range: 26–126 kPa
Resolution: 0.01 kPa
Accuracy: ±0.003 kPa at 25 °C
Equilibration: < 10 ms
Long-term drift: < 0.03 kPa/year, typical

Tilt
Range: 0°–180°
Resolution: 0.1°
Accuracy: ±1°

Communication Specifications

Output
SDI-12 communication

Data Logger Compatibility
METER ZL6 and EM60 data loggers or any data acquisition systems capable of 3.6- to 15.0-VDC excitation and SDI-12 communication

Physical Specifications

Dimensions
Diameter: 14 cm (5.5 in)
Height: 19 cm (7.5 in)

Operating Temperature Range
Minimum: –40 °C
Typical: NA
Maximum: 60 °C

Note: Barometric pressure and relative humidity sensors operate accurately at a minimum temperature of –40 °C

Cable Length
5 m (standard)
1.5 m (5-pin and 8-pin M12)
75 m (maximum custom cable length for additional cost)
Note: Contact customer support if a nonstandard cable length is needed

Connector Types
3.5 mm stereo plug or 3 stripped and tinned wires

Conductor Gauge
22-AWG / 24-AWG drain wire

Cable Diameter
0.165±0.004 in (4.20±0.10 mm), with minimum jacket of 0.030 in (0.76 mm)

Electrical and Timing Characteristics

Supply Voltage (VCC to GND)
Minimum: 3.6 VDC continuous
Typical: NA
Maximum: 15.0 VDC continuous
Note: ATMOS 51 must be continuously powered to work properly
Note: For the ATMOS 51 to meet digital logic levels specified by SDI-12, it must be excited at 3.9 VDC or greater.

Digital Input Voltage (Logic High)
Minimum: 2.8 V
Typical: 3.0 V
Maximum: 5.5 V

Digital Input Voltage (Logic Low)
Minimum: –0.3 V
Typical: 0.0 V
Maximum: 0.8 V

Digital Output Voltage (Logic High)
Minimum: NA
Typical: 3.6 V
Maximum: NA
Note: For the ATMOS 51 to meet digital logic levels specified by SDI-12, it must be excited at 3.9 VDC or greater.

Current Drain (during GPS fix)
Minimum: 5.0 mA
Typical: 8.0 mA
Maximum: 10.0 mA

Current Drain (during measurement, 75 ms/s)
Minimum: 0.2 mA
Typical: 1.0 mA
Maximum: 2.0 mA

Current Drain (while asleep, 925 ms/s)
Minimum: 0.2 mA
Typical: 0.3 mA
Maximum: 0.4 mA

Measurement Duration
Minimum:NA
Typical:75 ms
Maximum:100 ms