Read e-book online Field Guide to Lidar PDF
By Paul McManamon
This Field Guide covers some of the elements and kinds of energetic electro-optical sensors often called lidars within the textual content from uncomplicated 2nd direct-detection lidars to a number of subaperture artificial aperture lidars. different subject matters coated comprise receivers, apertures, atmospheric results, and applicable processing of other lidars. Lasers and modulation are offered when it comes to their use in lidars. The lidar variety equation in its many diversifications is mentioned besides receiver noise concerns that ascertain how a lot sign needs to be obtained to discover an item. This e-book is a convenient connection with quick lookup any element of lively electro-optical sensors. it will likely be precious to scholars, lidar scientists, or engineers wanting an occasional reminder of the right kind techniques or equations in convinced functions, and structures engineers attracted to gaining a point of view in this quickly transforming into know-how.
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Additional resources for Field Guide to Lidar
Real beam resolution, of course, is better at the shorter wavelengths. When selecting a lidar wavelength, the designer chooses one of the atmospheric lines that has low absorption. Many of those lines are spread across a fairly wide range from the visible to LWIR. Note that the graph does not assume a large presence of water vapor in the air. At high absolute humidity, the LWIR wavelength region does have significant absorption so should be avoided for those conditions. However, many other parameters will set the exact wavelength chosen.
However, it is often less expensive to mitigate mean-squared noise power. This can be done for both direct detection lidar and coherent lidar by using gain early in the detection process so that any noise after the gain is not as influential. The SNR for coherent lidar can also be increased by increasing the power of the LO. Because of the option of increasing LO power to mitigate noise effects, pre-amplification gain has not been used as often in coherent lidar as in direct detection lidar. The mean-squared signal current is ( 2 G2 <2 Ps2 ðdirect detectionÞ is ¼ 2 2 2hh G < PLO PS ðcoherent detectionÞ where G is pre-amplifier gain, < is detector responsivity, Ps is signal power, PLO is LO power, hh is heterodyne mixing efficiency, and hq e <¼ hn where hq is detector quantum efficiency, e is the charge on an electron, h is Planck’s constant, and n is the carrier frequency of the light.
Recently, there has also been some interest in ~2-mm wavelength and in the MWIR region. Atmospheric absorption at 2 mm and in the MWIR is also not significant, but scattering is less at longer wavelengths. Real beam resolution, of course, is better at the shorter wavelengths. When selecting a lidar wavelength, the designer chooses one of the atmospheric lines that has low absorption. Many of those lines are spread across a fairly wide range from the visible to LWIR. Note that the graph does not assume a large presence of water vapor in the air.
Field Guide to Lidar by Paul McManamon