Aerial drones (UAS) are convenient platforms for collecting multispectral camera images commonly used in the remote sensing industry. A multispectral camera on a drone saves the light spectrum reflecting off of objects at a much higher resolution than satellites and similar ground based tools. The different spectrums of light that a multispectral camera captures can tell you about the objects in the images. Just like humans can tell what objects are present based on the color of the objects, a multispectral camera can split the light up more precisely and show contrast better than we can see ourselves.

When a multispectral camera captures images that will be used for measuring the light reflecting off of objects you also need to measure both the ambient light spectrum and capture images of a calibration target, commonly called a reflectance reference standard. An ambient light sensor (ALS) records the distribution of light, so you know how each wavelength compares in intensity to one another. Images of the reflectance calibration target are used to correlate the camera pixel values to percent reflectance, allowing you to compare your reflectance data between locations and over time. An ambient light sensor and calibration target are required in order to completely calibrate the images from a multispectral camera.

Applications of Multispectral Cameras on Aerial Drones

Object Identification and Delineation

Identify specific objects such as particular plant species within a mixed scene.

Phenological Changes

Track reflectance changes of object(s) over time.

Physical Characteristic Analysis

Assess vegetation health (NDVI), leaf area (LAI), water stress (NDWI), etc.

Nutrient Management and Yield Prediction

Estimate leaf area (LAI), chlorophyll (CHI, TGI, NDRE), etc.

Damage Extent

Locate mold, pests, over/under application spray, malfunctioning water infrastructure, etc.

Multispectral Camera Solution from MAPIR

Using MAPIR Hardware on Aerial Drones

MAPIR offers cameras that do not have to be connected directly to a drone vehicle, which allows you to use them on most any system. If you wish to connect to the drone please see the information below:

Electrical Connection

Survey3 cameras contain an internal battery which you can keep charged by connecting to an external 5V power source. You can also remove the battery to reduce the weight when externally powered.

GNSS (GPS) Connection

The Survey3 comes with our Standard GNSS, which is a low cost solution but lacks the better positional accuracy from newer receivers. Our Advanced V2 GNSS uses the newest satellite technology to provide a stable lock even in obstructed areas. You can also provide the Survey3 camera with NMEA GPS messages from an external source, such as a drone's flight controller.

Camera Trigger Connection

The Survey3 camera is usually triggered to capture images using a PWM (GPIO) signal or using the camera's internal timer (intervalometer). 

Camera Setting Control

The Survey3 has a rear touchscreen LCD that makes adjusting settings quick and easy. While the drone is powered off you can also turn the camera's WIFI on and use our Survey3 Android application to adjust settings, trigger photo capture and view the live video feed.

Remote Live Video Viewing

Usually a drone is programmed with an autonomous mission when capturing images of an area, so a live view is not necessary. If you require a live preview you can get the live video feed from the Survey3 cameras over composite video (SD), HDMI (HD), USB (RTSP) and WIFI (RTSP).

Calibration Target Image Capture

While the light sensor is recording data an image of the reflectance calibration targets needs to be captured. You can manually capture the images prior to the drone flight or hover over the targets shortly after take-off. Once the calibration target images are captured the light sensor log will be used to adjust the reflectance data as the ambient light changes.

Light Sensor Measurements

The light sensor (DAQ-A-SD) can be mounted on the drone and provides the GNSS location data as well as triggering the camera(s). The light sensor can also remain on the ground when the drone will be flying in the same ambient light. The light sensor will save the ambient light spectrum every second to adjust the reflectance data in post processing of the images.

Below you can see that the effect from clouds can be removed when using our light sensor. The reflectance measurements are the same during both a cloudy and clear day. 

Types of Aerial Drones for Multispectral Image Capture