When LiDAR (Light Detection And Ranging) is used for mapping the shore line it is necessary to measure above and below the water level. This technique is used for monitoring meandering rivers and studying flood risk and erosion of the coast line. These environments have different requirements on a LiDAR system. An infrared laser is used for land and a green laser to penetrate the water (topo-bathymetric LiDAR). In good conditions, a depth of up to 50 meters can be monitored. This LiDAR application puts several requirements on the digitizer including high resolution amplitude capability (a Time to Digital Converter (TDC) is not enough) and high channel count to accommodate certain laser requirements.
SP Devices’ offers several models suitable for LIDAR applications:
- ADQ14DC-4C offers 4 channels at 1 GSPS with 14 bits resolution. The high vertical resolution allows for accurate images during underwater surveys. The four channels are available for multiple detectors connected to lasers with different wavelengths. The ADQ14 also allows for high throughput to the PC for fast scanning capabilities. Input impedance matching is also important, especially in an over voltage condition. The signals are strong and the over voltage protection circuitry often acts as a non-linear current sink. To avoid the non-linear condition and resulting large reflections during over voltage, the first stage of the ADQ14DC is linear and resistive. This means that there is an attenuation of reflections even in an over voltage scenario.
- ADQ412-4G also offers 4 channels, but at 2 GSPS per channel and with 12 bits vertical resolution.