Paul S. Banks

Comparison of flash lidar detector options

Abstract. Three lidar receiver technologies using the total laser energy required to perform a set of imaging tasks are compared. The tasks are combinations of two collection types (3-D mapping from near and far), two scene types (foliated and unobscured), and three types of data products (geometry only, geometry plus 3-bit intensity, and geometry plus 6-bit intensity). The receiver technologies are based on Geiger mode avalanche photodiodes (GMAPD), linear mode avalanche photodiodes (LMAPD), and optical time-of-flight lidar, which combine rapid polarization rotation of the image and dual low-bandwidth cameras to generate a 3-D image. We choose scenarios to highlight the strengths and weaknesses of various lidars. We consider HgCdTe and InGaAs variations of LMAPD cameras. The InGaAs GMAPD and the HgCdTe LMAPD cameras required the least energy to 3-D map both scenarios for bare earth, with the GMAPD taking slightly less energy. We comment on the strengths and weaknesses of each receiver technology. Six bits of intensity gray levels requires substantial energy using all camera modalities.

A comparison flash lidar detector options

This paper will discussion multiple flash lidar camera options and will compare sensitivity by calculating the required energy to map a certain area under specific conditions. We define two basic scenarios, and in each scenario look at bare earth 3D imaging, 3D imaging with 64 grey levels, or 6 bits of grey scale, 3D imaging with 3 return pulses from different ranges per detector element, and 3D imaging with both grey scale and multiple returns in each detector. We will compare Gieger Mode Avalanche Photo-Diodes, GMAPDs, Linear Mode Avalanche PhotoDiodes, LMAPDs, and low bandwidth cameras traditionally used for 2D imaging, but capable of being used for 3D imaging in conjunction with a rapid polarization rotation stage.

3D sensor development to support EDL (entry, descent, and landing) for autonomous missions to Mars

TetraVue is developing a MegaPixel-class 3D camera system that uniquely addresses autonomous spacecraft requirements for a situational awareness sensor during the planetary landing phase. TetraVues system uses a novel approach to FLASH LIDAR which utilizes existing commercial off-the-shelf (COTS) focal plane arrays in a single aperture module. This makes the system flexible enough to adapt to different resolution requirements without reinventing the hardware architecture or develop new imaging sensors with custom readout circuitry. Since the system uses a nanosecond-class laser as an illumination source, similar to a strobe, the data is insensitive to any discernable cross-motion which make it ideally suitable for landing site selection during the horizontal coast phase.

Comparing flash lidar detector options

Lidar (light detection and ranging) is a method of surveying based on pulsed laser light that is becoming very common. It is used by the military and by many commercial applications, such as 3D mapping and navigation in autonomous cars and unmanned air vehicles. For these applications, sensitive lidar detectors are essential. But there are different types of lidar detection schemes, with corresponding strengths and weaknesses. Here, we compare three lidar receiver technologies using the total laser energy required to perform a set of imaging tasks (a more detailed description is available elsewhere1). The tasks are combinations of two collection types (3D mapping from near and far), two scene types (foliated and unobscured), and three types of data products (geometry only, geometry plus 3-bit intensity, and geometry plus 6-bit intensity). The receiver technologies are based on indium gallium arsenide (InGaAs) Geiger mode avalanche photodiodes (GMAPDs) (see Figure 1), both InGaAs and mercury cadmium telluride (HgCdTe) linear mode avalanche photodiodes (LMAPDs), and optical time-of-flight (OTOF) lidar using commercial 2D cameras. This last method combines rapid polarization rotation of the image and dual lowbandwidth cameras to generate a 3D image. We chose scenarios to highlight the strengths and weaknesses of the various lidars. Table 1 summarizes the energy required for various imaging modalities. For the case of the InGaAs LMAPDs, we actually carried two bandwidth settings, but in the table we list only the bandwidth setting that required lower energy. GMAPD cameras operate with a low probability of return (i.e., reflection) on a single pulse, but require multiple coincident returns from the same range. The GMAPD cameras do well with bare-earth 3D mapping and 3D imaging through trees. In grayscale situations, the GMAPD cameras use somewhat more energy. The advantages of the GMAPDs are the following: they are thermoelectrically (TE) cooled; they are low energy per pulse, high-rep-rate lasers, Figure 1. Schematic illustration of a diffused-junction planar-geometry avalanche diode structure. This is the structure for one of our detector options, the Geiger mode avalanche photodiode (GMAPD). The electric field (E) profiles at right show that the peak field intensity is lower in the peripheral region of the diffused p-n junction than it is in the center of the device. SiNx: Silicon nitride. i-InP: Indium phosphide p-i-n diode. i-InGaAsP: Intrinsic (i.e., this region of the semiconductor wafer is not intentionally doped either por n-type) indium gallium arsenide phosphide.