Agricultural Measurements and Monitoring
In agricultural environments, plants and crops exhibit UV-VIS, NIR and color characteristics of interest to researchers, whose goal is to improve yield, quality and other characteristics. Ocean Optics spectrometers and accessories are compact, robust and easily configured for the field or research lab for immediate, in situ analysis. The data captured can have enormous value in identifying areas for sample improvement.
Our miniature spectrometers have been configured for a wide range of agricultural sample measurements including photosynthesis in leaves, upwelling and downwelling measurements in relation to crop health, and color as an indicator of fruit maturation.
Example Setup: NIR Reflection
Overview
Spectral reflectance measurements can provide information about sample colors and textures. Also, reflectance can reveal compositional information about the sample material, since light that is not reflected from a sample is absorbed due to its chemical composition, scattered or transmitted.
Very smooth surfaces have high specular reflection, which means all the incident light is reflected in the same direction (angle of reflection = angle of incidence). Rough or matte surfaces have diffuse reflection, which means the incident light gets scattered in all directions. Most surfaces are in-between, with a combination of specular and diffuse reflectance.
Spectrometer
Our NIRQuest spectrometers are a good choice for NIR reflection, with both 512-element and 256-element InGaAs array options available covering various ranges from ~900-2500 nm. In this setup we’ve selected a NIRQuest256-2.1 (900-2050 nm) with a 25 µm slit. An optional order-sorting filter (OF1-RG830, transmits >830 nm) is also available.
Sampling Optics
A reflection probe is great for making quick measurements and for applications where a small spot size needs to be sampled, and can measure either specular or diffuse reflectance. The downside is that a reflection probe illuminates and detects from the same direction, so it sees only part of the reflected light. Measurements made with a reflection probe are relative measurements.
The illustration here shows a 400 µm reflection probe (QR400-7-VIS-NIR) and the RPH-1 probe holder. The holder positions the probe at either 45° for diffuse reflection or 90° for specular reflection. For curved surfaces, we recommend substituting one of our CSH holders for the RPH-1.
There are alternatives to a reflection probe for sampling. An integrating sphere like the FOIS-1 is recommended if the reflectivity of the sample appears different when the angle at which it is illuminated is varied. This occurs for rough surfaces like fish scales, grains and seeds. For samples where a very high intensity light source is required, the combination Vivo light source-diffuse reflection stage is a good option.
For illumination, we used the HL-2000-HP-FHSA high-power tungsten halogen light source (360-2400 nm). The powerful light output (20 W versus 5 W for the standard source) is especially important for NIR measurements. To complete the setup, we added a WS-1-SL reflectance standard as a reference and OceanView spectroscopy software.
| NIRQuest256-2.1 | NIR spectrometer (900-2050 nm) with Grating NIR2 (900-2100 nm) and a 25 µm slit |
| HL-2000-HP-FHSA | High-power tungsten halogen light source (360-2400 nm) with filter holder, shutter and attenuator |
| QR400-7-VIS-NIR | Premium-grade reflection probe (6-around-1 fiber design), optimized for VIS-NIR response, 2 m length |
| RPH-1 | Fixture for holding 1/4″ (6.35 mm) diameter reflection probes |
| WS-1-SL | Diffuse reflectance standard |
| OceanView | Spectroscopy software |
NIR analysis can be used to distinguish absorbance characteristics of water and protein molecules in various samples.
Spectral characteristics of leaf samples offer insight into plant health and environmental adaptability.
Spectral data for corn kernels reveals differences based on sampling location and other variables.
Fruit maturity and the effects of the peel are among the factors affecting NIR diffuse reflectance spectra of mangoes.
For crops covered with a skin, longer wavelengths used for NIR analysis are weakly absorbed and pass through the skin to measure the flesh beneath.
