Stanford EE259 I Camera principle of operation and architectures, image formation I 2023 I Lec. 19

04 Feb 2024 (9 months ago)

Coherent Lidar

Coherent lidar systems use a coherent optical receiver and can measure both range and velocity, while direct detection lidar can only measure range.
Coherent lidar systems can be frequency modulated (FMCW) or phase modulated (PMCW).
FMCW lidar uses triangular chip waveforms to address the large Doppler shifts.
The coherent receiver extracts the conjugate multiplication of the transmitted and received signals.
The range (R) can be calculated as c * Tau / 2, where c is the speed of light.
The relative radial velocity can be calculated as -FD * Lambda / 2, where Lambda is the wavelength of the transmitted signal.
PMCW lidar uses phase-modulated ranging codes instead of triangular waveforms.
DSP for PMCW lidar is more complicated than FMCW lidar due to the presence of Doppler shift.

Flash lidar uses an array of photodiodes to capture a time-of-flight image, and the direction of arrival (DOA) is determined by the geometry of the pixels and optics.
Scanning lidars, such as multi-beam spinning lidars and MEMS scanners, determine DOA based on the fixed elevation angles of the laser beams and the known rotation angle of the scanner.
DOA estimation in lidar is generally simpler compared to radar and does not require significant DSP overhead.

Imaging is the process of capturing and recovering visual quantities from light.
The history of photography dates back to the 1800s, with early techniques such as bitumen of Judea and the daguerreotype process.
The daguerreotype process, invented by Louis Daguerre in 1839, produced high-quality images but required long exposure times and could not be easily reproduced.
William Talbot's calotype process, developed around the same time, allowed for multiple prints from a master negative and eventually evolved into modern analog photography.
The first digital camera was invented in 1975 at Kodak but was not commercialized until the 1990s.