Modified Multispectral Sensors
Modified sensors are created by placing a filter on a standard visual sensor, which collects three bands of light at once through the same lens. Various filters allow for the capture of different combinations of spectral bands. The most common formats sacrifice one of the visual bands to record near-infrared information (NIR). For example, an R-G-NIR filter sacrifices blue for near-infrared energy (~700 - 800 nm).
Multiband Multispectral Sensors
A multiband multispectral sensor simultaneously collects several individual bands instead of a single combination of three bands, as with standard or modified visual sensors. Where you might need to fly multiple drone flights with various modified sensors to capture all the multispectral data you need, you can collect everything in a single drone flight using a multiband sensor.
Typically reserved for crop science and research applications, hyperspectral sensors are like multiband multispectral sensors, in that they collect light data in multiple bands. However, hyperspectral sensors collect light in a series of 100-to-200 narrow bands--about 5-10 nm in width--to attain a high level of performance in spectral and radiometric accuracy.
The datasets produced by hyperspectral imagers are in the form of a three-dimensional hypercube in which two dimensions represent the spatial information (x,y) and the third dimension representing the spectral information. You can use this detailed spectral information to identify subtle differences in vegetation, minerals and other materials.
Processing Multispectral Sensor Data
By uploading multispectral sensor data into PrecisionAnalytics Agriculture, our mapping and data analytics platform, you can transform the various bands of multispectral data into indices that indicate vegetation health and stress. Indices require varying amounts of spectral data.
For example, a basic Normalized Difference Vegetation Index (NDVI) can be applied to basic red-green-blue (RGB) visual imagery captured by a regular camera. However, NDVI has its limitations. To gain a more accurate measure of crop health, you can deploy a multiband multispectral sensor, that includes near-infrared and infrared wavelengths of light, enabling you to run a Normalized Difference Red Edge (NDRE) vegetation index. This is better for mid- and late-season crops, which have greater accumulated levels of chlorophyll and multiple layers of vegetation.
Choosing a Multispectral Sensor
So, choosing a multispectral sensor to deploy on your drone often comes down do your desired analysis and the vegetation index it dictates is best suited to the use. In some cases, a simple visual sensor and NDVI output will do. But, when greater clarity is required, such as in the case of mid- and late-season crops or areas of interest that variable soil, a more sophisticated vegetation index will call for you to deploy a multiband multispectral sensor on your drone.