Title of Paper: Hybrid Digitizer for Ultrahigh Dynamic Range LIDAR
Principal Author: Dr. Jack Syage
Abstract: We report on a proprietary method called the Hybrid Digitizer (HD) for extending the dynamic range of a high-speed analog-to-digital converter (ADC) by as much as several orders of magnitude compared to existing technology. This work addresses data processing techniques to increase usefulness of raw data for airborne science instruments. Through high-speed data transfer, programmable signal processing, and signal gain control, a transient ADC digitizer can be operated in a single-photon detection mode while simultaneously detecting strong signal in the normal manner. The only alternative to achieving a similar dynamic range is the use of an ADC and a pulse counting system in tandem. The theoretical basis of the method was bench-tested and documented using model data. Demonstration instruments were developed and in-field testing conducted on an atmospheric LIDAR system and on a laboratory time-of-flight mass spectrometer (TOFMS) system. A competitive test was performed whereby the HD system was installed on a LIDAR system that had both ADC and pulse counting systems. LIDAR returns were collected on all three data acquisition systems simultaneously. The HD method demonstrated data quality and dynamic range matching the combined response of the ADC and pulse counting systems. However, the HD system is about 1/10 the size and cost of the conventional method and provides seamless data from the weak to strong signal limits. We are now increasing the data flow rate to achieve high repetition rate operation (>100 Hz) and multichannel detection (currently 4 channels) in a laptop size system. For NASA requirements in LIDAR and laser range finding applications, this new technology can lead to more than an order of magnitude greater range without any significant changes in hardware. For airborne remote sensing, the HD technology provides greatly increased capability as well as enables more compact design and a reduced cost.