Lidar Intensity Return

Lidar intensity data can be supplied as a separate image file (usually a TIFF), containing intensity images across all returns.

Depending on the manufacturer of the lidar sensor, this can be either an 8, 10 or 12-bit intensity map (signal strength of the return signal). The raw signal is usually normalized for visualization - sometimes back to 8-bit grayscale (0-255 counts), which can be readily viewed without image degradation (the maximum DICOM grayscale level being 465). It is used primarily to provide additional visual acuity for the point cloud or model.

In many cases laser intensity return images are especially useful for breakline detection & extraction when generating DTMs as well as for capturing and classifying features. They can also be used as the basis for other image-product generation using various "lidargrammetric" techniques.

Unless otherwise specified, pseudoreflectance images supplied are qualitative only, and do not contain radiometrically calibrated data. Image contrast uniformity will be provided within the tolerance specified by the sensor manufacturer from which the data was acquired.

Image Products

Active vs Passive Imagery

Unlike "passive" imagers (eg. conventional CCDs) which require ambient light in order to obtain an image, lidar intensity returns will look the same whether they were acquired day or night.

This is owing to the fact that lidar is an "active" sensor and will operate irrespective of ambient lighting. This key feature can be exploited to good use when attempting to visually discern features from photos that may be under or overexposed.

The lidar image will often appear correct even though the corresponding camera image may show shadows or glare.

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