# Why side looking?

While reading about remote sensing systems I notice about the side looking approach. I got the idea, it means the sensor does not look directly down to Earth. But I still do not understand why.

• Oblique radar/lidar/photography is used for many reasons the most useful is calculation of building heights from the ground to the highest point and frontages work, cell mask location etc.. It can also be cheaper to capture using drones, balloons etc (instead of aircraft). For humans we naturally see in stereo oblique.
– Mapperz
Commented Jan 13, 2018 at 16:23
• Youtube has this on their site google.com/… Commented Jan 14, 2018 at 17:40

Radar has to view obliquely so that the time delay of the echo is proportional to the distance across the swath. That's the only reason.

You can find a good explaination on the web site of the Center for Space Research (University of Texas at Austin): http://www.csr.utexas.edu/projects/rs/whatissar/rar.html

"A radar can only distinguish the returns from various targets based upon the arrival time of the received signals. A nadir-looking radar could not distinguish between two scatterers a and b (see Figure 2.2) that are equal distances from the sensor because a single incident wave front illuminates both points at the same instant, so the scattered returns from both points arrive at the receiving antenna simultaneously. This leads to an ambiguity in range for any right/left-symmetric, equidistant points. If the radar illumination is restricted to one side of the platform, the wave front illuminates the same two points at different times. Their scattered returns arrive at the sensor separated in time and are thereby distinguishable from each other."

• That page you linked is great but I cannot find its home page. Do you have a link for that? Commented Jun 6, 2023 at 3:14

Here are few reasons why:

1. Because in nadir looking radar, there's left-right ambiguity, i.e, radar system cannot differentiate equidistance left and right object.
2. There is very strong power reflected from surface in nadir looking system.
3. In side looking system; pulses hit the terrain at angle enhancing geological features like subtle folds and faults in the terrain.
4. Also, the time delay associated with this received signal, as with other pulse radars, gives the distance between target and radar in side looking system.

Additionally, For military application, flight can be operated in friendly territory, with capability to capture data in enemy's territory.