IEEE TRANSACTIONS ON INTELLIGENT TRANSPORTATION SYSTEMS, VOL. 13, NO. 1, MARCH 2012 413 Fig. 14. Transmitted and received signal frequencies. Fig. 15. Principle of measuring range and speed by FMCW. environments with moving objects, the FSF-laser-based range finder is unacceptable. 1) FMCW Realized by Waveform Modulation: Chirped pulse laser sources can also be realized by modulating the intensity of the continuous-wave (CW) laser [12]. The system has the same problem as described in the previous section. In contrast to this approach, the National Aeronautics and Space Administration (NASA) Langely Research Center [11] developed waveform-modulated FMCW laser radar to aid the NASA new space exploration initiative for manned and robotic missions to the moon and Mars. Fig. 15 shows the transmitted (solid) and the received (dashed) linearly chirped triangular modu- lation functions. The target range R and speed V can be obtained, providing that the two frequencies f D and f U of the beat signal are measured. The method measures the target range and speed with high preci- sion. However, the period of the triangular modulation function in [11] is as long as 5 ms; therefore, the scanning speed of the laser radar is no larger than 200 times per second. To improve the scanning speed, the transmitted signal length should be as short as possible. REFERENCES [1] A. Widodo and T. Hasegawa, “A vehicular driving assistant system using spread spectrum techniques,” IEICE Trans. Fundam., vol. E81-A, no. 11, pp. 2334–2340, Nov. 1998. [2] [Online]. Available: http://www.lambdaphoto.co.uk/pdfs/SumitomoMod- ulatorApplicationNote.pdf [3] [Online]. Available: http://www.tigerflare.com/ballistic-vest-review/ 346-lidar-radar-gun-review [4] [Online]. Available: http://en.wikipedia.org/wiki/LIDAR [5] T. Ando, S. Kameyama, and Y. Hirano, “All-fiber coherent Doppler lidar technologies at Mitsubishi Electric Corporation,” in Proc. 14th Int. Symp. Adv. Boundary Layer Remote Sens., IOP Conf. Ser., Earth Environ. Sci., 2008, vol. 1, p. 012011. [6] [Online]. Available: http://ams.confex.com/ams/pdfpapers/165128.pdf [7] S. Kameyama, T. Ando, K. Asaka, Y. Hirano, and S. Wadaka, “Compact all-fiber pulsed coherent Doppler lidar system for wind sensing,” Appl. Opt., vol. 46, no. 11, pp. 1953–1962, Apr. 2007. [8] [Online]. Available: http://www.mitsubishielectric.co.jp/lidar/ (in Japanese). [9] [Online]. Available: http://en.wikipedia.org/wiki/FMCW [10] K. Nakamura, M. Yoshida, T. Miyahara, and H. Ito, “Optical frequency- domain ranging by a frequency-shifted feedback laser,” IEEE J. Quantum Electron., vol. 36, no. 3, pp. 305–316, Mar. 2000. [11] [Online]. Available: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/ 20080026181_2008026116.pdf [12] P. Adany, C. Allen, and R. Hui, “Chirped lidar using simplified homodyne detection,” J. Lightw. Technol., vol. 27, no. 16, pp. 3351–3357, Aug. 2009. A Note on the ITS Topic Evolution in the Period 2000–2009 at T-ITS Manolo J. Cobo, Antonio G. López-Herrera, Francisco Herrera, and Enrique Herrera-Viedma Abstract—In this paper, we extend the study of the intelligent trans- portation system (ITS) topic evolution presented by Li et al. To do so, we apply an approach that combines both H-index-based performance analysis and science mapping to detect, visualize, and evaluate conceptual ITS themes and ITS thematic areas published by the journal IEEE TRANSACTIONS ON I NTELLIGENT TRANSPORT SYSTEMS during the decade (2000–2009). The primary consequence of this is the detection of three important thematic areas: COMPUTER-VISION and TRAFFIC- FLOW, which are related to research in ITS applied to vehicles, and AIRCRAFT-TRAFFIC, which is related to research in ITS applied to aircraft/airport. Index Terms—H-index, intelligent transportation systems (ITSs), knowledge visualization, science mapping analysis. I. I NTRODUCTION Recently, we have observed that the IEEE TRANSACTIONS ON I NTELLIGENT TRANSPORTATION SYSTEMS (IEEE T-ITS) is inter- ested in the analysis of intelligent transportation system (ITS) research contained in papers published in the journal [2]–[4]. In [3], Prof. F. Wang, Editor-in-Chief of the journal, provides a first approach to study the journal publications and their impact during the period 2000–2009. In [5] a commissioned group of researchers presents a bibliographic analysis of the papers published in the journal during the past decade by identifying the most productive and high-impact authors, institutions, and countries/regions. Then, in [1], an analysis of the collaboration patterns and the ITS topics’ evolution of the journal are presented. To develop the ITS topic evolution study presented in [1], the authors use the author-provided keyword cooccurrence network and cluster the keywords to topics by using the Girvan–Newman algorithm [6]. Then, they present a brief analysis of the evolution of the most Manuscript received December 15, 2010; revised July 5, 2011; accepted August 27, 2011. Date of publication September 30, 2011; date of current version March 5, 2012. The Associate Editor for this paper was F.-Y. Wang. The authors are with the Research Center on Information and Communi- cations Technology, University of Granada, E-18071 Granada, Spain (e-mail: mjcobo@decsai.ugr.es; lopez-herrera@decsai.ugr.es; herrera@decsai.ugr.es; viedma@decsai.ugr.es). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TITS.2011.2167968 1524-9050/$26.00 © 2011 IEEE