State of the LiDAR Profession, Sensors, Collection, and Calibration

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The LiDAR profession is constantly in flux. The sensor technology is continually changing for better or worse. The calibration process is adapting to these continuous changes and the collection has become more efficient which provides additional value for the users of the data and has provided efficiencies and opportunities for the profession. The innovation of focal plane LiDAR has provided additional opportunity for many as it relates to getting large projects collected in a timely manner. The linear mode sensors continue to provide value for most clients and is still an important tool within the profession.

Last year when the focal plane LiDAR (Geiger Mode and Single Photon) where introduced, significant concern was raised from the linear-mode holders. It wasn’t clear how this technology would affect the profession. It has become clear what will happen, this technology is here and will be a part of our profession until the next big thing comes along. A recent sensor evaluation conducted by the USGS was very fair and balanced as it related to both the Geiger Mode and Single Photon sensors. These sensors are referred to as Focal Plane LiDAR for the purpose of this article, and conventional discrete LiDAR is referred as Linear Mode LiDAR. It was clear that the Focal Plane LiDAR sensors performed differently in variety of land classifications such as urban and vegetation but the accuracy was very good and complimentary to current specification and requirements. It was also stated that the evaluation was done on a previous generation of the technology and that the latest technology is preforming better which is encouraging. It should be noted that the Geiger Mode LiDAR operates at 1064 nanometers (red Laser) and the Single Photon operates at 532 Nanometers (Green Laser). The biggest Linear Mode LiDAR but can get higher most recent development as it relates point densities as a result of the photon to Focal Plane LiDAR is that Hexagon purchased Sigma Space which opens the door for two well-funded predominate players in this space for now. It will be interesting to see who will come out of the wood work to also play in this space, but there is always someone in their garage building a bullet with your name on it. It should also be noted that the Geiger Mode and Single Photon technology, as they stand now have very distinct advantages to each other and the particular application they are used for requires some understanding of what each does well. This is not saying that in the very near future and maybe at the time this article is published that the advantages will not be very similar in nature. Dont discount the possibility at this point because in only a year this technology has come a long way and cautious optimism should be changed to optimism.

It is clear that the collection rates and efficiencies of Geiger Mode LiDAR is significantly better than Linear Mode based on the photon technology used, attitudes and speeds the sensor can be operated at, generally speaking. How does the cloud cover and weather conditions play into this equation? Single Photo LiDAR operates at similar heights as Linear Mode LiDAR but can get higher point densities as a result of the photon technology, so how does this compare? Typically speaking, The Geiger mode LiDAR can collect an area 10 to 15 times faster while achieving the same point spacing. The Single Photon LiDAR can collect the same area approximately 3 times faster than linear mode LiDAR at similar attitudes. This information is based on current systems in use. Recently, Teledyne Optech released a slick that indicated that the Galaxy has the potential to be 7 more times more efficient then the Geiger Mode LiDAR in the Washington, D.C. area. How could this be? This study was done using NOAA data for Ronald Reagan National Airport over a 2 year period. The study looked at the collection of 2, 8, and 20 points per meter (ppm) for both systems. For QL2 data the Geiger Mode LiDAR would operate at 45,000 feet AGL with a ground speed of 450 Knots and the Galaxy would operate at 7,316 feet AGL with a ground speed of 140 Knots and the swath width would be 25,000 feet and 8,448 feet respectively. The weather plays an important factor when considering collection efficiencies. This is the main basis for this study because LiDAR can’t see through the clouds and typically the cloud decks are below 45,000 feet. The Geiger mode LiDAR can fly lower than 45,000 feet. It would be required to fly at 27,000 feet to get 8ppm and 13,000 feet for 20ppm. Also, it has been said that the Focal Plane sensors collect significantly more points at any altitude than is actually used and the points are thinned to represent the desired point sample spacing. It seems that there is a case for using Linear Mode LiDAR versus a Focal Plane LiDAR based on the associated application.

The cost associated with operating the platforms for these sensors need to be considered as well. The Geiger Mode sensors are operated using jets were as the Linear Mode sensors are operated using fix wing aircrafts. It can then be inferred based on the flying heights of the Single Photon sensor would be flown using fixed wing aircraft. The profession is obviously disrupted by this new Focal Plane technology as it relates to traditional Linear Mode technology. The Linear Mode technology has established itself as a very viable mature technology to provide solutions for a vast array of applications and the concern is understandable that Linear Mode LiDAR manufactures have as it relates to the introduction of the Focal Plane LiDAR technology. It is important to embrace the new technology as an additional tool for providing solutions and solving problems. When Linear Mode LiDAR was introduced it was pimped as an alternative to photogrammetry and survey but in reality it complimented and still does compliment these technologies. This is probably the case for Focal Plane LiDAR based on several factors even though it will take the place of Linear Mode in some cases.

Optech continues to push the envelope of innovation with the recent MAPPS Technology Innovation award and Grand Award for the world’s first multispectral LiDAR sensor. Titan uniquely enables multi-application capability from a single sensor design, including high-resolution bathymetry, vegetation mapping and classification, and high-precision topographic mapping. However, the recent release of their wide-area mapping sensor, ALTM Galaxy, has really pushed Linear Mode sensor performance and collection efficiency to a whole new level. For the first time ever, a dynamic FOV is used to maintain consistent point distribution in variable terrain. This is done by creating swath widths that are the same width on a mountain peak as on a valley bottom.

By doing so, flight lines can be moved further apart, thereby improving data quality, reducing collection costs, and increasing data processing throughput. Actual field survey results have yielded efficiencies as high as 30-40% over conventional fixed-FOV sensor designs.

More recently, Optech provided a sneak preview of its latest sensor offerings known as Eclipse, the first fullyautonomous mapping solution for small platform’ low-altitude installations. Including both an active and passive sensor configuration, this new sensor features operator-less functionality with no training required for reliable and effortless data collection. It provides a mid-market solution for entry-level surveyors, as well as a low-price entry point for small area and corridor jobs.

Finally, Optech has released the first fully-integrated data pre-processing platform for LiDAR and image data handling. Leveraging least squares algorithms and photogrammetric block adjustment capability, Lidar Mapping Suite (LMS) is a production survey workflow that automates sensor calibrations and quantifies data accuracies across the entire project space. The legitimate fusion of high-accuracy LiDAR and image data is fast becoming a reality.

Riegl’s answer to the competition is the LMS-Q1560 and the VQ-880-G. The LMS-Q1560 is a two channel high altitude LiDAR sensor intended for topographic mapping and the VQ-880-G is a Topo/bathy LiDAR sensor. The LMS-Q1560 features the ability to have up to 10 pulses in the air at one time. The sensor can operate to altitudes up to 15,500 feet AGL. It features multiple-time-around (MTA) processing, echo digitization and waveform analysis. The VQ 880-G is an upgrade to its predecessor the VQ 820-G which was used for the Hurricane Sandy Bathymetric Survey conducted by NOAA which included collection for the majority of the east coast of the United States. Riegl continues to provide a strong suite of fully automated calibration and processing software and the waveform based sensor technology continues to provide LiDAR providers with a very reliable solution for their clients.

Leica aka. Hexagon continues to expand their offering through statergic technology acquisitions and continued internal technological development based on their ALS technology. Leica’s latest offerings are the ALS80-HP/-CM and DragonEye. Additionally, Leica, much like Optech and Riegl, offer a topo/bathymetric solution called the Chiroptera. Leica is now offering LSS which provides fully automated calibration correction within the initial processing software package. It would appear that this is currently available with the DragonEye and Chiroptera sensors but it is unclear if this is now available for the ALS sensors. Please contact Leica to understand the full capabilities of this software. The ALS80 provides a fully upgradable 1.0MHz pulse rate sensor. This sensor comes in three models, the CM which is designed for high density Corridor mapping, the HP which is stated to be used for general purpose mapping and the HP which is designed for the professions highest flying heights. The DragonEye is an airborne sensor with 2 oblique topo LiDARs, two 80mp digital cameras and one 5 megapixel quality control camera. The LiDAR is set at +/- 14 degrees and +/- 20 degrees perpendicular which is designed to maximize vertical surface definition and minimize shadows in the resulting data set.

The LiDAR profession has come a long way in the last five years. The development of the fully automated calibration and processing software packages is a welcomed addition to the profession. This provides the data end users much stronger and accurate data sets with the absences of inherent hardware errors, such as flight line missmatches. Additionally, the manufactures have greatly improved the in-flight interface to better detect potential issues and provide indications of data quality during collection in real-time. The Geiger-mode data provider uses a process similar to an AT solution which provides an excellent solution to this problem as well. We continue to see affects as it relates to the GSS-IMU solution but this has also improved and hopefully in the next few years it continues to improve and resolve itself so this headache is less prevalent. Overall, the technology continues to improve exponentially, providing better data and better results at a more competitive price.

Jill Wrenn is currently a Senior Field Operator for Merrick & Co. located in Greenwood Village, Colorado. Her experience includes extensive field experience including GPS survey, LiDAR and Digital Imaging Sensor operation, testing and troubleshooting sensors. She has a thorough understanding of the LiDAR production process as a result of past experience as a LiDAR production Manager.
James (Jamie) Wilder Young CP, CMS-L, GISP is currently a Senior Geomatics Technologist for Merrick & Co. located in Greenwood Village, Colorado. His experience includes all aspects of LiDAR including sensor development, applications development, data acquisition, data processing and project management.

A 2.321Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE