Light Detection and Ranging

Lidar also LIDAR, or LiDAR is a method for determining ranges by targeting an object or a surface with a laser and measuring the time for the reflected light to return to the receiver. It can also be used to make digital 3-D representations of areas on the earth’s surface, clouds and ocean bottom by varying the wavelength of light. It has terrestrial, airborne, and mobile applications.

Lidar is an acronym of “light detection and ranging” or “laser imaging, detection, and ranging”. It is sometimes called 3-D laser scanning, a special combination of 3-D scanning and laser scanning. The received light is converted to electrical signals using a sensor and then converted to digital for processing. Data acquisition and signal processing in the sensors require high sample rate, high vertical resolution digitizers.

XA-500M

Data Acquisition

The output from the optical sensor is converted into a digital signal using Analogue to Digital Convertors (Adcs). These are often sampling at millions of samples per second and triggered from the timing signals of the system which sends the transmit pulses along the fibre. The accuracy of the sampling and triggering clocks determines some of the resolution and accuracy of the whole measurement system. Therefore it is essential to use high quality components for these with excellent signal to noise and spurious free dynamic range.

Adc boards from Interconnect Systems Inc (ISI) provide all of these features. The boards also offer high bandwidth host connections so that continuous streaming of samples can occur to the host computer. Popular boards in this range include the XA-160M and the XA-500M which offer 160MSPS and 500MSPS Adc’s respectively. Many of our boards also include Digital to Analogue Convertors (Dac’s) for pulse generation if required.

Flexible trigger pattern facilities are useful as well which allow the backend acquisition to only capture samples from set periods after each trigger pulse allow the processing system to only process samples from “interesting” periods of time which represent set ranges along the fibre. All of the XA and FMC modules in the ISI product line offer pulsed pattern triggering.

FPGA Processing

The data rate from the sensor is often Millions or Billions of samples per second. This puts a large burden on the processing backend so it is useful to make use of custom logic in an FPGA. FPGA’s are excellent at “fast, simple” calculations such as filtering and converting between the time and frequency domain with FFT’s. FFT’s are often used in DAS/DVS and can be implemented in the custom logic on the XA and FMC modules. Entegra’s engineering team has already delivered several FPGA designs.

GPU Processing

Graphical Processing Units have come a long way and are useful for high speed processing, especially as the processing can be designed in software rather than register transfer logic. There are a lot more software engineers on the market than logic engineers! Platforms such as NVIDIA’s Xavier with GPU and CPU offer an excellent platform for DAS/DVS systems. The XA modules have software drivers for use under Ubuntu on the Xavier.

Array of Kintex Ultrascale and Virtex Ultrascale FPGA devices