NDVI Sensor

NDVI Sensor

At METER, we think you should spend less time on complexity and more time doing what matters. Apogee NDVI sensors are easy-to-use. And the best part? They’re pre-configured for use with the ZENTRA system, so you’re instantly up and running.

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Low cost—low maintenance

By focusing on just two relevant bands, it’s possible to make an accurate multiband radiometer for a fraction of what a full-spectrum spectroradiometer costs. Apogee NDVI sensors are multiband radiometers that combine an ultra-rugged form with sophisticated cloud data delivery for an unbeatable price-to-performance ratio. They’re inexpensive enough to deploy multiple sensors simultaneously, so you can maximize spatial coverage and explore spatial and temporal variability in canopy structure and function.

Deploy for months or even years

Most spectrometers are delicate and expensive, making long-term field deployment risky. Apogee NDVI sensors are built for long-term exposure to the elements. Encased in a durable housing with an epoxy fill, they are watertight, weatherproof, and have fully sealed optics. Mount them on a fence post, tripod, or a meteorological tower. They’re rugged enough to leave in the field for an entire growing season or longer.

Field ready and radiometrically calibrated

Each sensor is radiometrically calibrated to a NIST-traceable standard. Readings are output in units of radiant flux density. Calibration information is stored on board the sensor, so you never have to worry about keeping track of calibration coefficients.

Collect data and monitor remotely

To simplify your workflow, Apogee NDVI sensors are plug-and-play with ZL6 data loggers, which means automatic sensor recognition and zero programming. ZENTRA Cloud lets you monitor remote sites in near-real time from any internet-connected device. Observe field conditions, check and configure sensor and system function, or download data from the comfort of your home or office.

Work less. Measure more.

Apogee NDVI sensors are part of a complete system of affordable, easy-to-use sensors, loggers, and software that require little maintenance and put near-real-time data at your fingertips, so you can publish more and work less.

METER is trusted by

University of Idaho
Brigham Young University
Temple University
Campbell Scientific

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Power supply 5.5 to 24 V DC
Calibration factor (reciprocal of sensitivity) Custom for each sensor and stored in firmware
Calibration uncertainty ± 5 %
Output range SDI-12
Wavelength ranges Red detector = 650 nm ± 5 nm with 65 nm FWHM
NIR detector = 810 nm ± 5 nm with 65 nm FWHM
Measurement range 2x full sunlight
Measurement repeatability Less than 1 %
Long-term drift Less than 2 % per year
Response time Less than 0.6 s
Field of view 180°
Directional (cosine) response ± 2 % at 45°; ± 5 % at 75° zenith angle
Temperature response Less than 0.1 % per C
Housing Anodized aluminum body with acrylic window
IP rating IP68
Operating environment -40 to 70 C; 0 to 100 % relative humidity
Dimensions 30.5 mm diameter, 34.5 mm height
Mass (with 5 m of cable) 140 g
Cable 5 m of shielded, twisted-pair wire with TPR jacket and stainless steel connector

Prop 65 warning

Warranty 4 years against defects in materials and workmanship
Data logger compatibility (not exclusive) METER EM60 series, ZL6 series, ZSC, ProCheck, Campbell Scientific


Can I check downward-facing NDVI sensors output using a white panel test?
Yes, you could check downward-facing sensor response in the field on a sunny day using a white panel. Ideally, a Spectralon panel should be used. The SRS field stop calibration check should be done with the field stop sensors pointing down at an angle toward a white Teflon panel or Spectralon panel, so that the field of view is totally encompassed by the white panel. Then, with the hemispherical sensors pointing up to collect irradiance data at the same location and time (with no obstructions in the field of view), radiance values * pi (3.14) should be approximately equal to irradiance values.

Radiance = Irradiance/pi
Irradiance = Radiance * pi
What is the calibration equation of my NDVI sensor?
Because the response of the NDVI sensor is linear, the calibration is a simple multiplier that converts the raw readings to a calibrated value. There is an offset that is set to account for the noise readings that occur when the sensor is in complete darkness (dark offset). Both of these values are sensor specific and vary to some degree. A firmware update protects the calibration coefficients because they are stored in an area of the flash memory that is not touched during an update.
Why does the NDVI calculation show no results if the sensor wavelength output is zero? Is the sensor bad?
The sensor is not bad in this case. The NDVI calculation returns no results when data are zero in the denominator.
Can I use NDVI sensors at the plant level?
Yes, you can use NDVI sensors at the plant level for field application where there is natural sunlight. Make sure there are no shadows in the measurement area, or remove the data during shady or dark conditions. The problem with shady conditions is that the data are not reliable. You may need more sensor replications at the plant level if you see more variation.

If you plan on using a non-natural light source, this could be a big unknown about the effects of light intensity over time (intensity and distance changing over time). You would need to control these variables or measure them. For this reason, we recommend that the NDVI sensors be used in the field with natural sunlight (field instruments only).
What are some applications for NDVI sensors?
  • Intercepted photosynthetically active radiation
  • Leaf area index
  • Phenological stages of plant development
  • Biomass accumulation
  • Ground-based monitoring of vegetation density
  • Drought indication
  • Altered precipitation studies for drought tolerance
  • Canopy health/senescence
  • Spring canopy green-up
  • Ground truthing remotely sensed NDVI
What is the area of measurement?
It depends on the angle and the height the sensor is installed. Below is an example. The Apogee calculator is a good resource for determining the area of measurement. Use the 36 degree (18 degree half angle) sensor.

Field of view:

The field of view (FOV) is reported as the half-angle of the apex of the cone formed by the target surface (cone base) and the detector (cone apex), as shown below, where the target is defined as a circle from which 98% of the radiation detected by the radiometer is emitted.

Sensor FOV, distance to target, and sensor mounting angle in relation to the target will determine target area. Different mounting geometries (distance and angle combinations) produce different target shapes and areas, as shown below.
How do I calculate NDVI?
Calculate NDVI as:

NDVI = (ρNIR − ρred) / (ρNIR + ρred)

where, ρred and ρNIR are percent reflectances in the red and near infrared (NIR). ρ at each waveband is calculated as radiance/irradiance at each waveband, where radiance is reflected radiation intensity in that waveband and irradiance is incoming radiation intensity in that waveband.

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