LiDAR Range Equation

In calculating the required energy, or power, to obtain a measureable return with a LiDAR, an engineer can divide the calculation into two parts. The first part is the calculated intensity of the reflected laser light from the target. This result can be stated in terms of the number of photons returned to each detector in a certain period of time. The second part calculates how much energy, in photons, is needed in each detector to measure the returned signal. For the second part, we have to compare the returned energy to the noise. We discuss the second part of this in Chapter 6, which concerns LiDAR receivers. For a given noise, we can set a threshold that results in a certain probability of both detection and false alarm. The first part of this calculation—how many photons are returned—is usually called a link budget calculation. The second part of the calculation is associated with the receiver sensitivity. There are many different types of receivers, as discussed in Chapter 6. This chapter focuses primarily on the link budget portion of the calculation. For the calculations in this chapter, it is assumed that a certain number of received photons is required in a given period for the receiver to detect the return signal. Chapter 6 provides more detail on receiver sensitivity and probabilities, which depend on the type of receiver being considered.