Coherent operation

Analogue sampling and chirp generation may be driven by the external 12 MHz reference supplied by the clock board. Additionally, as the chirp repetition period is set digitally and fixed throughout, the inter-chirp period is stable. is opens up the possibility for phase-sensitive measurement such as range-Doppler pro- cessing. Figure 6.11 shows a distortion in a single elevation slice captured using AVTIS. is blurring can be aributed to the Doppler shi caused by a rapidly ro- tation of material during a rock-fall event. While this large event is clearly visible in the range profile, range-Doppler processing has the potential to detect smaller events which may be obscured beneath the larger bulk terrain response.

Given the operating range at which AVTIS typically operates, achieving a high chirp repetition rate sufficient to achieve a high maximum unambiguously resolvable velocity may be challenging. In order to ensure an overlap between transmied signal and target return necessary for effective down-conversion, the signal time-of-flight must be short in comparison to the chirp duration. Assum- ing back-to-back chirp generation and a 95% overlap, the maximum observable Doppler frequency would be 2500 Hz. If chirp overlap were relaxed to 75% then this frequency would increase to 12500 Hz, corresponding to a maximum unam- biguously resolvable velocity of approximately 10 metres per second. However, if

Figure 6.11:Single elevation slice captured from AVTIS. Blurring in range can be seen due to the Doppler-shi which results from the rotational motion of a rock-fall event. Image courtesy of Dr David Macfarlane.

it is only necessary to differentiate motion in the scene from the static background then aliasing in the velocity transform may be tolerable. At shorter stand-off dis- tances, below 1 km, shorter chirp periods could be chosen while maintaining a high percentage overlap.

Unfortunately, owing to damage to the frequency multiplier in AVTIS-2, it was not possible to perform Doppler measurements with AVTIS-2 in the time available.

6.7 Conclusions

A significant increase in processing throughput was achieved by implementing processing routines based upon the work developed with NIRAD and IRAD, as outlined in chapter 3. As a result of these enhancements, radar processing occurs approximately in real-time. A scan scheduling feature, critical to the autonomous operation of AVTIS-3, was developed which allows a number of different scan parameters to be set, which are executed in sequence. Resulting data is stored temporarily in a date and time-based folder structure, before being transferred to a remote base computer.

File transfer soware was developed in order to ensure the reliable transfer of captured radar data under potentially unreliable network conditions. Data transfer was implemented using standard Windows API functions to copy data to a remote network share. Successful transfer of data is assured through use of a custom checksum verifier which communicates using standard TCP networking. e checksum verifier runs on the base computer and generates the checksum using the standard MD5 cryptographic function, along with the file size in bytes. Aer transfer is completed, the file size and MD5 signature are compared with a match indicating successful transfer. Partial transfers are detected and transfer resumes without the need to redundantly transfer the existing data. In the case of a mismatch, the transfer is repeated. Data is never removed from the control computer unless a successful transfer can be verified.

A ies Clima laser disdrometer was deployed in order to provide a source of reliable rainfall data, including drop size distribution, for correlation with radar observations. A low power data logger was developed which interfaces with the distrometer via RS-485 and stores captured data to a MicroSD card.

was tested and installed in its remote site on Windy Hill. Located approximately 3 km from the Soufrière Hills volcano, AVTIS-3 is capable of fully automated operation under solar power. Since the conclusion of this fieldwork, the soware developed as part of this doctoral work has proven to be robust. AVTIS-2 was deployed to obtain more complete DEM coverage of the lava dome.

Based on the development of the clock generator, outlined in section 3.4, a compact 5 x 5 cm clock generator was developed for AVTIS. e board is con- trolled through USB using a simple serial protocol which allows fine control of the triggering frequency. e board integrates aenuator control and power mon- itor functionality which were previously performed by an additional USB digital acquisition device. e board firmware is easily reprogrammable over its USB connection, allowing low level trigger behaviour to be reconfigured for new mea- surement types without the need for physical access to the radar head. is is of particular use in the case of AVTIS-3. e clock generator has been integrated and tested in both AVTIS-2 and AVTIS-3. Future work would certainly include an assessment of the performance of AVTIS-2 for performing Doppler analysis. If positive results were to be obtained from such testing, they could be deployed remotely to AVTIS-3.

Chapter 7

Conclusions and future work

7.1 Summary

e underlying aim of the doctoral work which has been presented in this thesis has been to advance the use of millimetre-wave radar in a number of applica- tions relating to security and remote sensing. While the work which has been presented in this thesis encompasses a several different themes within the field, they each represent an essential step towards realising this aim. In this final chap- ter, the important results from each of the preceding chapters will be summarised and potential future work will be discussed.