NDVI Sensor
Crop Circle ACS211

Crop Circle ACS-211 Active Canopy Crop Sensor

The Crop Circle ACS-211 active crop canopy sensor calculates the NDVI vegetation index as well as measuring basic reflectance information from plant canopies and soil.

Unlike passive radiometric light sensors, the Crop Circle ACS-211 is not limited by ambient lighting conditions — measurements can be made day or night due to its unique light source technology.

For on-the-go applications, the Crop Circle ACS-211 sensor can be mounted to virtually any type of vehicle to remotely sense and/or map plant or crop canopy biomass while driving through a field. The compact size and low weight design allows the Crop Circle ACS-211 to be easily adapted for pole-mounted and handheld applications. Information produced by the sensor can be utilized to quantify the impact of nutrients, water, disease or other growing conditions on plants or crops.

Crop Circle ACS-211


The ACS-211 incorporates two optical measurement channels. The sensor simultaneously measures crop/soil reflectance at 670 nm and 780 nm. A unique feature of the ACS-211 sensor is its ability to make 3D NDVI measurements: an industry first. The sensor accomplishes this by assessing the approximate height of the plant canopy. The height measurement is then used to scale the NDVI measurement, accordingly. This new NDVI measurement technique helps to reduce the saturation effect often encountered when using the classic NDVI measurement at high biomasses.


 Using the Holland Scientific GeoSCOUT X datalogger, data can be easily and quickly recorded. Geospatial sensor data are stored on an internal 4GB SD flash card. All recorded data are saved using a comma-separated-variable text format for easy import into third-party GIS mapping and analysis software.


Two measurement channels

3D NDVI measurement

Make measurements day or night

Measurements not influenced by fluorescent or other AC light sources

Wide measurement range — 0.25m to 2.5m

Rugged—dust and water resistant

Low noise performance

Fast data output rate

Low power operation

Crop Circle ACS-211


  • Sensor-to-Canopy Range: Typically 10 in (25 cm) to over 96 in (244 cm)
    Field-of-View: ~40 degrees by ~8 degrees
    Active Light Source: Modulated polychromatic LED array
    Photodetection: Two channel silicon photodiode array
    Optical Measurement Bands: 670 nm and 780 nm

  • Sample Output Rate: 5 samples per second in autosend mode
    Operating Range: 0 to 50 oC
    Communication Interface: RS-485 multi-drop (bidirectional communication); RS-232 (autosend, output only)
    RS-232 Serial Communication: 38400, no parity, 8 data bits, 1 stop bit
    Power: 7 to 17V DC @ ~210 mA
    EMC Certifications: TBD

  • Enclosure: Injection molded polycarbonate
    Environmental: IP68 for dust and water resistance
    Weight: 0.9 lb (430 gm)Sensor Mount: (2) M6 X 1 threaded holes in base of sensor spaced 1.25 in (3.18 cm)
    Dimensions: Width 3.5 in (8.9 cm), Length 7.9 in (20.1 cm), Height 1.9 in (4.8 cm)
    Serial/Power Connector: Twelve pin Deutsch, O-ring sealed

  • Crop Circle ACS-211 Handheld System includes: Crop Circle ACS- 211, GeoSCOUT X, extension pole apparatus, cables, storage case, charger and user’s guide

    Crop Circle ACS-211 Mapping System includes: Crop Circle ACS- 211, GeoSCOUT X, cables, storage case, mounting plate and user’s guide