Nearmap NIR captures data in four separate spectral bands - red, green, blue, and near infrared spectrum, facilitating advanced analytics such as vegetation health assessment and assisting with land use classification. Regular aerial surveys enable the tracking of changes over time to support monitoring and planning activities in constantly changing environments.
This article describes some of the technology behind Nearmap NIR.
Nearmap camera system
Nearmap's new camera system has the capability to provide Near Infrared (NIR) imagery. Our camera system is equipped with two cameras:
- The first one integrates an RGB sensor that can detect and respond to light between the wavelength range of 400 and 700 nanometers.
- The second one has an NIR sensor that can detect and respond to light between the wavelength range of 700 to 1000 nanometers.
Together, these cameras produce Vertical imagery with a Ground Sample Distance (GSD) of 30cm per pixel allowing for detailed analysis and identification of ground features, vegetation reflectivity, and changes to the built environment.
NOTE: Currently, Nearmap NIR does not produce Oblique imagery.
Image processing
Once the imagery is captured, it undergoes two steps of post-processing, namely:
- Geometric post-processing
- Photometric post-processing
RGB vs NIR
Geometric post-processing
As mentioned earlier, two different cameras are employed to capture RGB and NIR imagery. The imagery captured by these cameras does not align perfectly and requires geometric correction. This is done by first constructing a Digital Elevation Model (DEM) from the imagery of the RGB camera and projecting the NIR imagery onto this. The resulting imagery is projected back to the RGB camera's viewpoint to correct the misalignment.
Photometric post-processing
Photometric post-processing is a two-step process:
- The first step involves the correction of light across the imagery to produce imagery with uniform brightness. Without this correction, the image center tends to be brighter than its edges.
- The second step involves haze removal. Because of the altitude from which the imagery is captured, a significant portion of the light reaching the camera is scattered, which causes a haze resulting in images that appear bright blue.
NIR imagery is ready for offline delivery after these processing and some additional steps are completed.
