# Introduction to Radar Scattering Application in Remote Sensing and Diagnostics: Review
## 3 Radar Fundamental Equations and Parameters
studied the back-scattering produced by different kinds of plants in case of both dry soil and moist content. In particular, they observed plants on soil with different moisture employing radar at X and Ku bands, and, more specifically, frequencies between 8 and 18 GHz. They concluded that, in the case of a smooth surface, the backscatter was very sensitive to a near nadir incident angle, while, in the case of rough surfaces, the backscatter was almost independent of the incident angle [34]. The quality of a radar can be assessed also by its ability to identify the difference between target location and size [35; 36]. Since signals transmitted by radars and reflected by objects find it difficult to enter the radar receiver, targets may remain undetected, and produce therefore a false negative, or signal interference can produce a false positive, also called false response or false alarm. Well-trained radar operators are not usually tricked by signal interference. Interference cannot be easily fixed by an automatic system of detection and tracking; it is usually necessary to detect and remove interference pulses before entering the automatic radar detector and tracker. [PERSON] et al. studied several radars control and signal processing steps to overcome the interference. They reported an effective procedure to reduce the impact of Radio Frequency Interference (RFI) on the oceanographic measurements [37]. [PERSON] et al. described the eigenanalysis methods used to overcome the interference problem [38; 39]. A further parameter that is worth mentioning in this context is the radar receiver's sensitivity, which can be defined by the unavoidable noise at its input. This parameter has a great impact on the radar performances, and radar engineers often use an amplifier as the first stage of the receiver to improve the desired pulses and reduce noise and other unwanted signals. In particular, a designer tries to exaggerate the detection of weak signals using a \"matched filter\", i.e., a filter that maximizes the signal-to-noise ratio at the output of the receiver. The matched filter has an explicit mathematical formulation which depends on the input signal shape and the recipient noise character [40; 41; 42]. Finally, it is worth mentioning how radar images are affected by a target surface texture: radar images are composed of pixels and each pixel represents the amount of backscattered wave received from the surface of a given object. A surface can, in general, appear to a radar either as smooth or \begin{table}
\begin{tabular}{c c c} \hline \hline \# & **Band Designation** & **Frequency Range** \\ \hline
1 & HF & 3–30 MHz \\
1 & VHF & 30–300 MHz \\
2 & UHF & 300–3000 MHz \\
3 & L & 1–2 GHz \\
4 & S & 2–4 GHz \\
5 & C & 4–8 GHz \\
6 & X & 8–12 GHz \\
7 & Ku & 12–18 GHz \\
8 & K & 18–27 GHz \\
9 & Ka & 27–40 GHz \\
10 & V & 40–75 GHz \\
11 & W & 75–110 GHz \\
12 & mm & 110–300 GHz \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Radar frequency bands according to IEEE standards. \begin{table}
\begin{tabular}{c c c c} \hline \hline \# & **Main Scattering Area** & **Frequency Band** & **Frequency** \\ \hline
1 & Leave Twigs & \(X-Band\) & 8–12 GHz \\
2 & Leaves and small branches & \(C-Band\) & 4–8 GHz \\
3 & Branches & \(L-Band\) & 1–2 GHz \\
4 & Trunk & VHF & 30–300 MHz \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Tree elements correspondence to the frequency of different radar bands. as rough, depending on both the frequency employed and the incidence angle. A smooth surface tends to reflect the energy in a single direction and generally away from the radar. For this reason, smooth surfaces tend to appear very dark in radar images. A rough surface, instead, tends to scatter an incident field in every direction; thus, a bigger portion of the radiation is statistically sent back to the radar system, and the images appear lighter. Therefore, in radar imaging, calm body water usually appears as dark.