## 4 Field Data Collection and Ranging Experiment  
To verify that the proposed circuit and method are valid, we used an engineering prototype for field data acquisition and ranging comparison. The selected thermistor in the \(-\)40-80 \({}^{\circ}\)C temperature range corresponded to a resistance range of 500-205 K\(\Omega\). Single-channel sampling rate \(S\) was set to 100 KSPS, and integration time \(t\) was 1 ms. The data control and processing terminal was integrated into the FPGA of the DBD. To facilitate the trial, we used an RF cable connection. The thermistors were installed in the ISL payload of the DBD and the RF channel and then put into the temperature box for data acquisition. The effective control of the temperature box is \(-\)30-60 \({}^{\circ}\)C, which is within the temperature tolerance of an industrial-grade chip. The rate of change in the temperature was 0.5 \({}^{\circ}\)C/min. The test scenario is shown in Figure 6.  
The left side of Figure 6 shows the ISL ground-support test system, which includes the time-frequency module, ground ISL signal transceiver of the baseband module, RF channel module, and industrial computer. The middle panel in Figure 6 shows the automatic temperature box, and the data acquisition and processing PC is located at the top of the temperature box. The right side of Figure 6 shows the ISL payload equipment, which is put into the temperature box, followed by the DBD, RF channel, and the baseband and channel as a unit. We separately collected four groups of transmitted and received data for the DBD and RF channel. The flow processes of 16 groups of measured data are shown in Figures 7-10. Figure 6: Test scenarios of the field data collection and ranging comparison. The temperature reference shown in Figures 7-10 is 14 \({}^{\circ}\)C, i.e., \(V_{c}\) is 6500. We set the order of fitting polynomial \(k\) equal to 20. Subpanels (a-d) in Figures 7-10 show the delay data curves measured four times and the corresponding fitting curves. According to Equation (6), subpanel (e) shows \(\overline{\overline{\tau_{i}^{T}}}\) or \(\overline{\overline{\tau_{i}^{R}}}\), the arithmetic means of the delay data measured four times and the corresponding fitting curves. According to Equation (7), \(\overline{\overline{\tau_{c}^{T}}}\) and \(\overline{\overline{\tau_{c}^{R}}}\) corresponding to \(V_{c}\) of 6500, and subpanel (f) shows \(\Delta\tau_{i}^{T}\) or \(\Delta\tau_{i}^{R}\), i.e., the final delay compensation curves. Figures 7 and 8 show the DBD transmission- and reception-delay measurement data preprocessing, respectively. Figures 9 and 10 show the RF channel transmission- and reception-delay measurement data preprocessing, respectively. Figures 7-10 show that the DBD is less affected by temperature, and its transmission and reception delays change at the level of 1 ns. Meanwhile, the RF channel, because it contains more analog nonlinear components, is more affected by the temperature. Its transmission and reception delays change at the level of 5 ns. Figure 8: Digital baseband (DBD) reception-delay measurement data preprocessing. (**a–d**) the reception-delay data measured four times and the corresponding fitting curves; (**e**) the arithmetic means of the delay data measured four times and the corresponding fitting curves; and (**f**) the final reception-delay compensation curves of the DBD. Figure 7: Digital baseband (DBD) transmission-delay measurement data preprocessing. (**a–d**) the transmission-delay data measured four times and the corresponding fitting curves; (**e**) the arithmetic means of the delay data measured four times and the corresponding fitting curves; and (**f**) the final transmission-delay compensation curves of the DBD. After the data processing, from Equation (8), the corresponding converted temperature compensation data were stored in the ROM of the FPGA. Then, we put the DBD and the RF channel together in the temperature box and controlled the temperature box at 14 \({}^{\circ}\)C and \(-\)30-60 \({}^{\circ}\)C for the delay compensation comparison test.