# UAV-Borne Profiling Radar for Forest Research
## 2 FGI-Tomoradar Development  
UAV/small plane based bistatic antenna profile radar termed Tomoradar was constructed at FGI. A pencil-beam FM-CW scatterometer provided the backscattering properties of a target as a function of range. A two-antenna configuration in the Ku-band provided higher sensitivity for all polarization modes compared to a single antenna solution. Both backscattered amplitudes from horizontal and vertical polarization channel were recorded to provide a polarimetric waveform radar image. The advantages of Tomoradar over the HUTSCAT system are shown in Table 1.  
It can be observed that except for lower spatial resolution, Tomoradar easily outperforms HUTSCAT. In addition to the higher range resolution and modulation frequency and lower weight and power consumption, the fast Fourier transform (FFT) calculation can be performed by the software in real time in Tomoradar. Thus, after the down-conversion of the received RF echo to an intermediate \begin{table}
\begin{tabular}{c c c} \hline  & **Tomoradar** & **HUCAT** \\ \hline Modulation frequency \(f_{\text{mod}}\) & 163 Hz & 60 Hz \\ Distance range & 10–300 m & 8–167 m \\ Range resolution & 15 cm & 65 cm \\ Centre frequency & 14 GHz (21 cm) & 9.8 GHz (3.1 cm) \\  & & 5.4 GHz (5.6 cm) \\ Spatial resolution & two-way antenna beamwidth \(<\)6\({}^{\circ}\) & 3.8\({}^{\circ}\) (9.8 GHz) \\ Polarization & Full & Full \\ A/D converter & 12 bits & 12 bits \\ Recoded Data & IF amplifier data & FFT results only \\ FFT & Software-based & Hardware-based \\ Georeference Accuracy & 1 cm + 1 ppm & Unspecified \\ Power Consumption & 20 W & several hundred watts based on the configurations \\ Weight & Less than 5 kg & approximately 50–100 kg, including antenna support \\ Data rate & 2.5 M/S & 80 KB/S \\ \hline \end{tabular}
\end{table} 
Table 1: Technical Specification Comparison between Tomoradar and HUCAT. frequency (IF) signal, high-pass filtering and IF amplification, the raw IF signal can be sampled at a high sampling rate by a digitizer, which is synchronized to the original triangular waveform used to modulate the microwave oscillator. The system weight and power consumption of Tomoradar are significantly lower than HUTSCAT as Table 1 presents, which enables Tomoradar's use on a UAV platform. The UAV platform offers following advantages comparing with other airborne platforms:  
* UAV platform is more cost-effective than helicopter or fixed-wing platforms, and the field test cost is considerable lower than for other manned aircrafts. * There are fewer regulatory restrictions on the UAV platform, such as test permission applications. In Finland, the lightweight Mini-UAV platform is allowed to perform field tests less than 200 m in operation altitude without special permission in unrestricted areas with line of sight operation condition. In addition, UAV-borne Tomoradar offers enhanced flexibility in empirical tests of theoretical research. * The UAV platform is particularly suitable for the spatial resolution of Tomoradar. Single-tree-level forestry investigation requires much lower operation altitude--tens meters, based on current spatial resolution (6 degrees). * Finally, because the current Tomoradar is not equipped with a mechanical scanning supporter, it can only collect the profile data along the trajectory rather than a scanning imaging radar. The operational efficiency using the helicopter platform is low: only the backscatter reflected by the targets at nadir direction with a few meters swath width can be collected. To investigate a normal plot (i.e., 32 \(\times\) 32 m\({}^{2}\)), assuming the flight height is 50 m; at least 7 parallel scans are required with current antenna configuration, which involves extra effort for the helicopter pilot. Meanwhile, the flight route can be defined with most flying control programs for the UAV platform. Moreover, the scanning supporter might cause a polarization-change problem.