CROPSCAN, Inc.

Multispectral Radiometers

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The CROPSCAN, Inc. Multispectral Radiometers (MSR) were developed to improve the assessments of various factors on plant health and yield. Visual assessments are subjective, laborious, tiresome and expensive. Use of CROPSCAN, Inc. MSR Systems make assessments objective, fast, easy and relatively inexpensive.

• Features
• Theory of Operation
• System Components
• Applications
• Radiometer Models
• Additional Information

FEATURES:

• Upward and downward facing sensors to measure both incoming and reflected radiation, nearly simultaneously, which allows for useful reflectance readings in lightly cloudy conditions down to about 300 Watts per square Meter incident irradiance.
• 3 Models:
  • MSR5, a 5-band LANDSAT Thematic Mapper compatible model (460-1750nm)
  • MSR87, an 8 narrowband wavelength model (460-810mm), and
  • MSR16R model with up to a maximum of 16 sensor bands in the 450-1750 nm region.
• Interfaces with the CROPSCAN DLC, a multichannel Data Logger Controller (communicates with laptop or notebook computers or hand held terminals via RS232 I/O port).
• Light weight and completely portable. Easily hand-carried from location to location or used in stand-alone unattended operation.

THEORY OF OPERATION:

Every substance emits, absorbs, transmits or reflects electromagnetic radiation in a manner characteristic of the substance. This is the underlying principle involved in all remote sensing. By measuring the quantity of radiation in each of the wavelengths, the characteristics of the substances can be defined. In practice, only certain selected wavelength bands need to be chosen to discriminate between selected characteristics of substances. For the CROPSCAN radiometer system, narrow band interference filters are used to select certain bands in the visible and near infrared (NIR) regions of the electromagnetic spectrum. This region is useful for quantifying the reflectivity of canopies as affected by stresses of various kinds. The NIR bands of 750-900 nm are particularly useful for detecting and estimating the severity of foliar disease of plants. Longer wavelengths in the NIR may be useful for estimating biochemical content of plants.

Typical Spectral Curves

SYSTEM COMPONENTS:

The CROPSCAN multispectral radiometer systems consist of a radiometer, DLC or A/D converter, terminal, telescoping support pole, connecting cables and operating software. The radiometer uses silicon or germanium photodiodes as light transducers. Matched sets of the transducers with filters to select wavelength bands are oriented in the radiometer housing to measure incident and reflected irradiation. Filters of wavelengths from 450 up to 1720 nm are available.

SYSTEM OPERATION:

In the field the radiometer is held level by the support pole above the crop canopy. The diameter of the field of view is one half of the height of the radiometer above the canopy. It is assumed that the irradiance flux density incident on the top of the radiometer (upward facing side) is identical to the flux density incident on the target surface. The data acquisition program included with the system facilitates digitizing the voltages and recording percent reflectance for each of the selected wavelengths. The program also allows for averaging multiple samples. Ancillary data such as plot number, time, level of incident radiation and temperature within the radiometer may be recorded with each scan.

Each scan, triggered by a manual switch or by pressing the space key on a terminal or PC, takes about 2 to 4 seconds. An audible beep indicates the beginning of a scan, two beeps indicate the end of scan and 3 beeps indicate the data is recorded in RAM. Data recorded in the RAM file are identified by location, experiment number and date.

The design of the radiometer allows for near simultaneous inputs of voltages representing incident as well as reflected irradiation. This feature permits accurate measurement of reflectance from crop canopies when sun angles or light conditions are less than ideal. Useful measurements of percent reflectance may even be obtained during cloudy conditions (cirrus to light stratus) with incident irradiance levels down to approximately 300 watts per square meter. In cumulus conditions (white puffy type) it is best to readings with the sun's rays are not obstructed by the heavy cumulus cloud. The ability for use in cloudy conditions can be advantageous, especially when traveling to a remote research site only to find the sun somewhat obscured by clouds.

APPLICATIONS:

Percent reflection of radiation of the various wavelengths is influenced by any condition that influences the normal growth of plants. The radiometer is therefore particularly useful as an objective and efficient means of estimating the effects of any condition that affects plant health, yield, or quality of the crop. Possible applications (customer or user responsible for model development) are:

• Inputs into models:
  • describing normal plant growth.
  • describing plant canopy color.
  • for estimating crop biomass.
  • for estimating biochemical content
  • for estimating crop yield components.
  • for estimating crop quality factors.
  • for estimating leaf area index.
  • for estimating crop yield and quality loss due to disease, insect infestation, air pollution, nutrient deficiencies, chemical phytotoxicity, etc.
• Evaluation of plant growth modifiers.
• Objective and efficient rating of foliar disease.
• Monitoring effects of herbicide activity.
• Soil amendment and fertility studies.
• Leaf feeding studies.
• Irrigation scheduling studies.
• Effects of drought on plant growth and yield.
• Characterization of different genotypes.
• Evaluation of experimental area variability.
• Land surface reclamation studies.
• Ground truth for Remote Sensing.

References to Publications/Presentations based on the use of CROPSCAN, Inc. MSR Systems

RADIOMETER MODELS:

MSR5

Size of housing - 80 X 80 X 100 mm. Made of brushed, anodized aluminum. Sensor bands similar to Landsat Thematic Mapper: 450-520 nm 520-600 nm 630-690 nm 760-900 nm 1550-1750 nm Flashed opal glass cosine diffuser covers incident irradiance measuring sensors. 28 degree field of view for reflected irradiation sensors.

MSR5 Spectral Bands (approximate visual colors) shown over typical green vegetation reflectance

MSR87

Size of housing - 80 X 80 X 100 mm. Made of brushed, anodized aluminum. Standard set of eight narrow sensor bands, centered at: 460 nm 510 nm 560 nm 610 nm 660 nm 710 nm 760 nm 810 nm Flashed opal glass cosine diffuser covers incident irradiance measuring sensors. 28 degree field of view for reflected irradiation sensors.

MSR87 Spectral Bands (approximate visual colors) shown over typical green vegetation reflectance

MSR16R

Size of housing - 80 X 80 X 100 mm, brushed, anodized aluminum. Accommodates up to 16 bands, in the 450 - 1750 nm region, to measure incident as well as reflected radiation. Can be ordered with down-facing sensors only, if to be used with a white reference panel (requires clear sky conditions). Flashed opal glass cosine diffuser covers incident irradiance measuring sensors. The housing is connected to a 32 channel multiplexer module, the MSR Cable Adapter Box (MSRCAB), by a 25 conductor cable. The MSRCAB is connected to the DLC by ribbon cables.

Available MSR16R Spectral Bands (approximate visual colors) shown over typical green vegetation reflectance. Up to a maximum of 16 of any of the following may be installed with order.

ADDITIONAL INFORMATION:

Select from the following for more information:

• Experimental Results
• Programs Included with System
• User Interface (Menu Flow Chart)
• Radiometer Specifications
• System Configurations

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