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Can LiDAR sensors collect near-infrared (NIR) data at the same time or does there need to be a separate NIR camera that is combined with the LiDAR data after collection?

Blue Marble makes reference to it in their latest release of global mapper: http://www.directionsmag.com/pressreleases/updated-global-mapper-lidar-module-now-supports-nir-lidar-data/444480

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    I've not seen a NIR LiDAR unit but it would be technically feasible, due to the very low energy of NIR it may not be able to go too high though - if such a device is manufactured I have not seen it. Lasers by nature are extreme monochrome (not just 'red' one wavelength of 'red') so normally to fill out RGB (and new to ASPRS 1.4 RGBI) values you would derive them from a raster.. I would expect that NIR values are raster derived rather than being a NIR laser itself. It sounds like they're saying now supporting LAS 1.4 which supports NIR. – Michael Stimson Jun 2 '15 at 4:07
  • yeah that sounds about right i would guess it is just regarding las 1.4. – gomapping Jun 4 '15 at 4:41
  • I find this topic really interesting, because the last release of LiDAR data in Spain was a nice surprise, because they point clouds that were acquired fot the whole country by the Government had also NIR information. As a consequence, each point in the cloud has not only x, y and coordinates but also an specific value of NIR. I am rally interested in knowing if you now any country that is doing the same, or at least are planning to incorporate the multispectral data capture at the same at time the LiDAR one. Thanks in advance. – Covadonga Prendes Pérez Aug 29 at 15:56
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The simple answer is that lidar sensors coupled with NIR cameras can collect point cloud data that can then have the NIR values "embedded" with them, the same way RGB values can be assigned to point cloud data collected with high res photos.

  • thanks, yeah that was what i figured, i just thought that maybe the laser intensity data was somehow processed or the laser changed to include ir. – gomapping Jun 4 '15 at 4:42
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LiDAR sensors are not "coupled" with NIR sensors. Most LiDAR devices are NIR sensors. A LiDAR works by emitting a LASER beam pulse in a single wavelength and measuring the travel time when the pulse returns to it. The receiving sensor can measure the intensity of one or several return for each pulse. Topographic LiDAR use wavelength in the NIR (most of the time 1550 or 1064 nm) for eye safety reasons. Bathymetric LiDAR use green (532 nm) in order to reduce absorption by water, but this can cause eye safety issues.

The intensity values are usually stored in the raw files as full waveform or for the main returns only. It is worth noting that the NIR value stored on a single return comes from a fraction of the emitted signal if the same pulse had several returns. Interpreting the intensity of multiple returns as a reflectance value of the observed surface is therefore tricky because the area of the surface contributing to this return is unknown.

Of course, it is possible to carry other sensors on the plane equipped with LiDAR (e.g. a multispectral sensor) in order to assign other spectral vules to the point cloud. But then you have more contraints on you flight (multispectral sensors are passive, so you can't use them during the night).

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