The alignment of the telescope-eyepiece pair and relay lenses using the Twyman-Green interferometer was conducted with the assistance of Dr. Karen J. Gordon in the Selex ES Laser Centre of Excellence. The field trials and the transceiver bore-sighting were performed with the assistance of Dr. Karen J. Gordon, Roger Pilkington and Dr. Philip Hiskett of Selex ES. The control software for the scanning mirrors was developed solely by Dr. Karen J. Gordon. Dr. Stephen Harding of Selex ES provided advice on laser safety and all safety documentation was written with help from Dr. Karen J. Gordon.
4.18 Conclusions
This chapter presented the initial stage of the experimental work performed with the scanned single-element system in bi-static configuration where the alignment of the system, timing electronics scheme and calibration of scanning mirrors were described.
172 Kilometre-range depth imaging in broad daylight using a single-element SPAD in a scanned bi-static configuration was demonstrated. An IRF was measured and confirmed depth resolution of < 30 cm where the limiting factor on the depth resolution was the laser pulse of 800 ps duration.
The acquired data allowed the energy budget model to be evaluated with the experimental data and confirmed that the experimental photon count rate is close to the theoretical prediction.
The analysed raw data was represented as a three-dimensional point cloud for different types of objects scanned over ~ 2.8 km and ~ 4.2 km and allowed three-dimensional features of the objects, such as the taper angle and radius of curvature of the chimney as well as the slope of the wall in respect to the line of sight, to be identified. In addition, imaging through a semi-transparent sheet of netting was demonstrated.
It has been shown that identification of a complex scene located kilometres away is possible with a total acquisition time of ~ 15 s for a 32 × 32 image. An investigation into the possibility of decreasing the total acquisition time using different data processing techniques in presented in Chapter 5.
Due to the limited access time in the roof laboratory a more in-depth evaluation of the system was not possible. It will, however, be presented in Chapter 5.
173
References
[1] J.J. Degnan, D. Caplan, “Performance of Liquid Crystal Optical Gate for Suppressing Laser Backscatter in Mono-Static Kilohertz SLR systems”, Proc. Of 15th Intern. Workshop on Laser Ranging, Australia (2007)
[2] A. McCarthy, X. Ren, A. D. Frera, N. R. Gemmel, N. J. Krichel, C. Scarcella, A. Ruggeri, A. Tosi, G. S. Buller, “Kilometer-Range Depth Imaging at 1550 nm Wavelength Using an InGaAs/InP Single-Photon Avalanche Diode Detector”, Opt. Express, 21, 19, pp. 22098-22113 (2013)
[3] http://www.princetel.com/datasheets/SMF28e.pdf
[4] http://www.tydexoptics.com/products/spectroscopy/oap_mirrors/
[5] Safety of Laser Products, British Standards, PD IEC TR 60825-14 (2004) [6] Safety of Laser Products, BSI Standards Publication, BS/EN/60825-1 (2014) [7] Manlight Laser, Instruction Manual
[8] A. Tosi, A. Della Frera, A. Bahgat Shehata and C. Scarcella, “Fully programmable single-photon detection module for InGaAs/InP single photon avalanche diodes with clean and sub-nanosecond gating transitions”, Rev. Sci. Instrum. 83, 013104 (2012)
[9] A. Tosi, A. Dalla Mora, F. Zappa, S. Cova, M. A. Itzler, X. Jiang, “InGaAs/InP Single-Photon Avalanche Diodes Show Low Dark Counts and Require Moderate Cooling”, Proc. SPIE, 7222, 72221G-1 (2009)
[10] HydraHarp400, Time-Correlated Single-Photon Counting system with USB Interface, Instruction Manual
[11] W. Becker, A. Bergman, G. Biscotti, A. Ruck, “Advanced Time-Correlated Single-Photon Counting Technique for Spectroscopy and Imaging in Biomedical systems”, Proc. SPIE 5340 (2004)
[12] https://www.google.co.uk/maps
[13] D.V. O’Connor, D. Phillips, “Time-Correlated Single-Photon Counting”, Academic Press (1984)
[14] http://zone.ni.com/reference/en-XX/help/371361J-01/lvanls/peak_detector/ [15] L.M. Chugani R.A. Samant, M. Cerna, “LabVIEW Signal Processing”, Prentice
and Hall (1998)
[16] W.J. Smith, “Modern Optical Engineering”, SPIE Press (2008)
[17] P.A. Hiskett, R.A. Lamb, “Design Considerations for High-Altitude Altimetry and Lidar Systems incorporating Single-Photon Avalanche Diode Detectors”, Proc. SPIE, 8033, 80330F-1 (2011)
174 [18] W.I. Newman, “Continuum Mechanics in the Earth Sciences”, Cambridge
University Press (2012)
[19] http://search.newport.com/?q=retroreflector%2063.5%20mm [20] E. Hecht, “Optics”, Adison Wesley (2005)
[21] I.I. Kim, B. McArthur, E. Korevaar, “Comparison of Laser Beam Propagation at 785 nm and 1550 nm in Fog and Haze for Wireless Optical Communications”, Proc. SPIE, 4214, 0277-786X/01 (2001)
[22] Jeremy Copley, Selex-ES Internal Report (2009) [23] Celestron C-GEM Series, Instruction Manual
[24] A. McCarthy, R.J. Collins, N.J. Krichel, V. Fernandez, A.M. Wallace. G.S. Buller, “Long-Range Time-of-Flight Scanning Sensor Based on High-Speed Time-Correlated Single-Photon Counting”, Appl. Opt., 48, 32 (2009)
[25] K.A. Stroud, D.J. Booth, “Engineering Mathematics”, 7th Edition, Palgrave McMillan (2013)
175
Chapter 5
Evaluation of the Transceiver in Mono-Static
Configuration with a Scanned Single-Element SPAD
Detector
5.1 Introduction
This chapter describes experimental results acquired with the lidar system operating in a mono-static configuration with the single-element SPAD (i.e. described as mode C in previous chapters). Details of the transmitter design, timing electronics, the alignment, bore-sighting and backscatter mitigation based on an electrical gating approach are described.
In order to assess the depth resolution of the system measurements of the instrumental response function and resolution tests were performed. A surface-to-surface resolution test is described where the peak finder technique applied to raw data and to a cross- correlation between a histogram and a normalised instrumental response function are compared. It was demonstrated that when the data is cross-correlated with the instrumental response function, surface-to-surface resolution increases, the quality of an analysed three-dimensional image increased and the total acquisition time decreases. Finally, depth images of different types of objects such as an electricity pylon, foliage, terrain and buildings acquired over distances between 800 m and 10.5 km are presented. In addition, image mosaicing of an object with up to 100 × 235 scan points is shown.