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Dr. Qassim Abdullah
Dr. Qassim Abdullah
Dr. Qassim Abdullah is an accomplished scientist with more than 37 years of combined industrial, research and development, and academic experience in analytical photogrammetry, digital remote sensing, and civil and surveying engineering. His current responsibilities include designing and managing … More »

Geiger Mode Lidar and Single Photon Counting Lidar: Immediate Threat or Gold Mine of Opportunities

 
November 20th, 2015 by Dr. Qassim Abdullah
Sample of SPCL data with density of 45 pt/m2 using Sigma Space Corp.  system, "HIRQLS".

Sample of SPCL data with density of 45 pt/m2 using Sigma Space Corp. system, “HIRQLS”.

Do not feel intimidated with the names, but Geiger Mode Lidar (GML) and Single Photon Counting Lidar (SPCL) are no different from any other lidar in the sense that they deliver point cloud data for light-reflective ground surfaces. In layman’s terms, GML and SPCL are lidar systems that utilize a Focal Plane Array concept that is similar to a digital camera. Instead of a single detector, as is the case with the current linear lidar, both GML and SPCL utilize an array of detectors to receive the split pulse. In these new lidar systems, each laser pulse gets split into multiple sub-pulses to increase the data density and ground resolution. Depending on the system architecture and optics design, the pulse gets split either on departure or after it reflects back before it reaches the detectors.

These systems are commercially available now and a few of them are used in a full-production environment, providing data with a nominal point density of 8-12 points per square meters or higher according to the manufacturer’s claim. Such new lidar collects dense point cloud data from a higher altitude, resulting in wider ground coverage and therefore higher productivity. Such lidar systems will enable data providers to routinely deliver data according to Quality Level 1 of the USGS–NGP and 3DEP specifications.

With the little information available about these new lidar systems, some may perceive the new technology as a threat to their current investment in the linear lidar while others see in it as a gold mine of opportunities. In my opinion, at least for the next five years, the new lidar will neither eliminate the need for the current linear lidar nor will it be the gold mine that some anticipate.

I believe the two lidar technologies, linear and GML/SPCL, will coexist for a while and in many cases will complement each other as users’ needs and specifications vary widely.

Here are the arguments behind my belief:

  1. The lack of intensity image: Because the GML and SPCL lidar systems use very low pulse energy, i.e. fewer photons, they lack the full wave form digitization capability and therefore the ability to create a real intensity image. Users who believe that the intensity image plays an integral role in their processing workflow will maintain ties with the current linear lidar and will follow a slow transition pattern to the new lidar, if they ever do. Some manufacturers produce what is called “relative reflectivity image” and they claim such an image can be used to replace the intensity image from the linear lidar. It will take a lot of convincing on the part of manufacturers for the users to accept such a claim, due to the lack of the full wave form information that shapes the radiometric resolution of the intensity image. At the end, data providers and their clients would have to decide whether the increased point cloud density will make up for the lack of intensity image.
  2. Continuous innovations in linear lidar: Although GML and SPCL lidar seem to be more productive than linear lidar, manufacturers of the latter are still surprising the market with innovations to increase the productivity of their systems. Point’s density from linear lidar is continuously improved over the years and it is hard to predict where it is going or if we are approaching its limit.
  3. The high cost and limited availability of GML and SPCL lidar: Only a few GML and SPCL lidar systems have been produced so far, and almost none of the manufacturers are willing to sell them to mapping companies who are interested in acquiring such systems. Manufacturers are trying to get appreciable return on their capital investments during their development efforts by providing acquisition services instead of selling operational units. The situation will rapidly change once one or more of the main manufacturers of the linear lidar decide to enter the race and start selling GML and SPCL lidar.
  4. The current investments in linear lidar systems: Data providers invested tremendous money over the years in the linear lidar systems and in training their work forces on its operation and data processing. Investments in airborne lidar systems take years to bring much-needed appreciable return. In addition, many of the current lidar systems are fully productive, and owners will be hesitant to invest in new lidar technology until their current investments are paid off and/or such new technology proves to clearly add to their productivity and profit margins.

Finally, although very little is known about them to many, Woolpert has participated in the development of an SPCL system and in the processing of its data over the last few years. My personal experience with the data accuracy and quality is very positive, and I would like to assure you that the GML and SPCL lidar systems are real and that technology are here to stay. It is just a matter of time before they become very popular.

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