{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,9]],"date-time":"2026-01-09T19:42:25Z","timestamp":1767987745634,"version":"3.49.0"},"reference-count":45,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2018,3,16]],"date-time":"2018-03-16T00:00:00Z","timestamp":1521158400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Remote Sensing"],"abstract":"<jats:p>Many coherent lidars are used today with aerosol targets for detailed studies of e.g., local wind speed and turbulence. Fibre-optic lidars operating near 1.5 \u03bcm dominate the wind energy market, with hundreds now installed worldwide. Here, we review some of the beam\/target physics for these lidars and discuss practical problems. In a monostatic Doppler lidar with matched local oscillator and transmit beams, focusing of the beam gives rise to a spatial sensitivity along the beam direction that depends on the inverse of beam area; for Gaussian beams, this sensitivity follows a Lorentzian function. At short range, the associated probe volume can be extremely small and contain very few scatterers; we describe predictions and simulations for few-scatterer and multi-scatterer sensing. We review the single-particle mode (SPM) and volume mode (VM) modelling of Frehlich et al. and some numerical modelling of lidar detector time series and statistics. Interesting behaviour may be observed from a modern coherent lidar used at short ranges (e.g., in a wind tunnel) and\/or with weak aerosol seeding. We also review some problems (and solutions) for Doppler-sign-insensitive lidars.<\/jats:p>","DOI":"10.3390\/rs10030466","type":"journal-article","created":{"date-parts":[[2018,3,20]],"date-time":"2018-03-20T06:57:11Z","timestamp":1521529031000},"page":"466","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":23,"title":["Coherent Focused Lidars for Doppler Sensing of Aerosols and Wind"],"prefix":"10.3390","volume":"10","author":[{"given":"Chris","family":"Hill","sequence":"first","affiliation":[{"name":"Malvern Lidar Consultants, Great Malvern, Worcestershire WR14 1YE, UK"}]}],"member":"1968","published-online":{"date-parts":[[2018,3,16]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Hill, C.A. (2015). Modern fibre-optic coherent lidars for remote sensing. Proc. SPIE, 9649.","DOI":"10.1117\/12.2197698"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1600","DOI":"10.1364\/AO.10.001600","article-title":"Signal-to-noise relationships for coaxial systems that heterodyne backscatter from the atmosphere","volume":"10","author":"Sonnenschein","year":"1971","journal-title":"Appl. Opt."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Lawrence\n              T.R.\n            \n            \n              Wilson\n              D.J.\n            \n            \n              Craven\n              C.E.\n            \n            \n              Jones\n              I.P.\n            \n            \n              Huffaker\n              R.M.\n            \n            \n              Thomson\n              J.A.L.\n            \n          \n          A laser velocimeter for remote wind sensing\n          Rev. Sci. Instrum.\n          1972\n          43\n          512\n          518\n         In their lidar (our Figure 1a) the received light must make at least one extra reflection after the beamsplitter. In a common UK terminology this is an autodyne lidar, because the backscattered radiation \u201cis collected by the telescope and allowed to reenter the laser cavity where it is amplified\u201d. The overlap of the reemerging radiation with the (BP)LO may or may not be stable and easily described\u2014this also depends on the active cavity mode structure and the radiation frequencies. Most fibre-optic lidars, including the one in our Figure 1b, are not intended as \u201cautodyne\u201d in this sense. The word has various meanings.","DOI":"10.1063\/1.1685674"},{"key":"ref_4","unstructured":"Lindel\u00f6w, P. (2008). Fiber Based Coherent Lidars for Remote Wind Sensing. [Ph.D. Thesis, Technical University of Denmark]."},{"key":"ref_5","unstructured":"Henderson, S.W. (2013, January 17\u201320). Review of fundamental characteristics of coherent and direct detection Doppler receivers and implications to wind lidar system design. Proceedings of the 17th Coherent Laser Radar Conference, Barcelona, Spain."},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Hao, C.H., Guo, P., Chen, H., Zhang, Y.C., and Chen, S.Y. (2013). Determination of geometrical form factor in coaxial lidar system. Proc. SPIE, 8905.","DOI":"10.1117\/12.2034667"},{"key":"ref_7","doi-asserted-by":"crossref","unstructured":"Jakeman\n              E.\n            \n            \n              Ridley\n              K.D.\n            \n          \n          Modeling Fluctuations in Scattered Waves\n          CRC Press\n          Boca Raton, FL, USA\n          2006\n         See chapter 4\u2019s review of random-walk models and partly developed speckle.","DOI":"10.1201\/9781420012163"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"530","DOI":"10.1088\/0305-4470\/7\/4\/016","article-title":"Single-interval statistics of light scattered by identical independent scatterers","volume":"7","author":"Pusey","year":"1974","journal-title":"J. Phys. A"},{"key":"ref_9","unstructured":"Banakh, V., and Smalikho, I. (2013). Coherent Doppler Wind Lidars in a Turbulent Atmosphere, Artech House."},{"key":"ref_10","doi-asserted-by":"crossref","unstructured":"Rye\n              B.J.\n            \n          \n          Spectral correlation of atmospheric lidar returns with range-dependent backscatter\n          J. Opt. Soc. Am.\n          1990\n          7\n          2199\n          2207\n         Here Barry Rye thanks the late Ken Hulme for emphasising the superposition of scattered \u201ccopies\u201d.","DOI":"10.1364\/JOSAA.7.002199"},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Siegman\n              A.E.\n            \n          \n          The antenna properties of optical heterodyne receivers\n          Appl. Opt.\n          1966\n          5\n          1588\n          1594\n\t\t   Siegman refers readers to his 1964 IEEE-MTT conference paper and to an unpublished memo by R E Brooks of the TRW company.","DOI":"10.1364\/AO.5.001588"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"4111","DOI":"10.1364\/AO.29.004111","article-title":"Receiving efficiency of monostatic pulsed coherent lidars. 1: Theory","volume":"29","author":"Zhao","year":"1990","journal-title":"Appl. Opt."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"637","DOI":"10.1364\/AO.41.000637","article-title":"Alignment tolerances for plane-wave to single-mode fiber coupling and their mitigation by use of pigtailed collimators","volume":"41","author":"Wallner","year":"2002","journal-title":"Appl. Opt."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"2022","DOI":"10.1109\/JQE.1982.1071488","article-title":"The influence of losses of hollow dielectric waveguides on the mode shape","volume":"18","author":"Tacke","year":"1982","journal-title":"IEEE J. Quantum Electron."},{"key":"ref_15","unstructured":"Kavaya, M.J. (2002). Coherent lidar: Factors of two among friends. NOAA Working Group on Space-Based Lidar Winds, NASA\/Langley Research Center."},{"key":"ref_16","unstructured":"Hill, C.A. (2010). Calibration and optical efficiency of fibre-based coherent lidars. UpWIND Report, Technical University of Denmark."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Lindel\u00f6w, P., Courtney, M., Parmentier, R., and Cariou, J.P. (2008). Wind shear proportional errors in the horizontal wind speed sensed by focused, range gated lidars. IOP Conf. Ser. Earth Environ. Sci., 1.","DOI":"10.1088\/1755-1315\/1\/1\/012023"},{"key":"ref_18","unstructured":"Cariou, J.P. (2010). Pulsed Coherent Lidars for Remote Wind Sensing, Remote Sensing Summer School at Ris\u00f8-DTU."},{"key":"ref_19","unstructured":"Cariou, J.P., and Boquet, M. (2010). LEOSPHERE pulsed lidar principles. Technical Report for UpWIND Work Package, Technical University of Denmark."},{"key":"ref_20","unstructured":"Hill, C.A., and Harris, M. (2010). Lidar measurement report. Technical Report for UpWIND Work Package 6, Technical University of Denmark."},{"key":"ref_21","unstructured":"Beuth, T. (2016). Analyse und Optimierung von Fokussierten LiDAR-Systemen f\u00fcr Windkraftanlagen (Analysis and Optimisation of Focused Lidar Systems for Wind Turbines). [Ph.D. Thesis, Karlsruhe Institute of Technology]."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"736","DOI":"10.1364\/JOSAA.15.000736","article-title":"Coupling efficiencies for general-target-illumination ladar systems incorporating single-mode optical fiber receivers","volume":"15","author":"Brewer","year":"1998","journal-title":"J. Opt. Soc. Am."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"5325","DOI":"10.1364\/AO.30.005325","article-title":"Coherent laser radar performance for general atmospheric refractive turbulence","volume":"30","author":"Frehlich","year":"1991","journal-title":"Appl. Opt."},{"key":"ref_24","unstructured":"Kavaya\n              M.J.\n            \n            \n              Henderson\n              S.W.\n            \n            \n              Frehlich\n              R.G.\n            \n          \n          Theory of CW lidar aerosol backscatter measurements and development of a 2.1-\u03bcm solid-state pulsed laser radar for aerosol backscatter profiling\n\t\t  This is Contractor Report CR-4347\n          NASA\n          Washington, DC, USA\n          1991\n         The \u201cprobe volume\u201d for a reasonably tightly focused Gaussian beam is estimated as \u03bb3(F\/D0)4 where F is focal distance and D0 is beam diameter at the lens. There are various acceptable versions of this in the literature (with different notations and factors of about \u03c0), such as (8\u03bb3\/\u03c02)(f\/wlens)4, but our \n        \n          \n\t\t  \n        8\n       \n       \u03bb\n    3\n   \n   \n    R\n    \n     lens\n\t \n   \n   \n    \n\t\n    4\n   \n   \/\n   (\n   \n    \u03c0\n    2\n   \n   \n    w\n    0\n   \n   \n    \n\t\n    4\n   \n   )\n   \n          \n        \n       in [1] seems misprinted."},{"key":"ref_25","unstructured":"Durst, F., Melling, A., and Whitelaw, J.H. (1981). Principles and Practice of Laser-Doppler Anemometry, Academic Press. [2nd ed.]."},{"key":"ref_26","doi-asserted-by":"crossref","unstructured":"Schulz-Dubois, E.O. (1982, January 23\u201326). Photon correlation techniques in fluid mechanics. Proceedings of the 5th International Conference, Kiel-Damp, Germany.","DOI":"10.1007\/978-3-540-39493-8"},{"key":"ref_27","unstructured":"A Renard et al., French patent 2 948 459 (24 July 2009), US 2011\/0181863 (23 July 2010); X Lacondemine et al., French patent FR 1202729 (12 October 2012), US 8,976,342 B2 (date of patent 10 March 2015). If we know the crosswind V and the chirp duration, we know the particle\u2019s distance from focus (though not whether it lies on the near or far side). If we do not know V, we need both duration and slope (measured, of course, at \u201csufficient\u201d CNR). These papers correctly explain the beam\/particle physics but there are minor problems: First, the radius of curvature is not shown decreasing (to a minimum at zR) and then increasing again at longer ranges from the waist; second, there is a language or translation difficulty in the US version at: \u201cIn other words, at the Rayleigh distance zR, the radius of curvature of the wavefronts is large and, as they move away from this point 205, their radius of curvature decreases\u201d. The French original is En d\u2019autres termes, au niveau de distance de Rayleigh zR, les fronts d\u2019onde sont tres incurv\u00e9s, puis en s\u2019\u00e9loignant de ce point 205, l\u2019incurvation diminue. But the curvature of the wavefronts, not their radius of curvature, is \u201clarge\u201d\u2014a local maximum\u2014at zR. I thank Xavier Lacondemine and Jean-Pierre Cariou for confirming that the English text is wrong here [1]. The French text is correct but en s\u2019\u00e9loignant de ce point 205 can be misinterpreted."},{"key":"ref_28","unstructured":"Baral-Baron, G. (2014). Traitements Avanc\u00e9s Pour L\u2019augmentation de la Disponibilit\u00e9 et de L\u2019int\u00e9grit\u00e9 de la Mesure de Vitesse 3D par LiDAR, dans le Domaine A\u00e9ronautique (Advanced Methods for Increasing the Availability and Integrity of Lidar Airborne 3D Velocimetry). [Ph.D. Thesis, Sup\u00e9lec]."},{"key":"ref_29","unstructured":"Mayo, W.T. (1975, January 22\u201324). Modeling laser velocimeter signals as triply stochastic Poisson processes. Proceedings of the Minnesota Symposium on Laser Anemometry, Minneapolis, MN, USA."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"3387","DOI":"10.1364\/AO.38.003387","article-title":"Interference of backscatter from two droplets in a focused continuous-wave CO2 Doppler lidar beam","volume":"38","author":"Jarzembski","year":"1999","journal-title":"Appl. Opt."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"1091","DOI":"10.1364\/AO.42.001091","article-title":"Lidar frequency modulation vibrometry in the presence of speckle","volume":"42","author":"Hill","year":"2003","journal-title":"Appl. Opt."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"969","DOI":"10.1364\/AO.40.000969","article-title":"Single-particle laser Doppler anemometry at 1.55 \u03bcm","volume":"40","author":"Harris","year":"2001","journal-title":"Appl. Opt."},{"key":"ref_33","unstructured":"Hill, C.A., Bennett, J., and Smith, D. (2009, January 22\u201326). Airport trials with the Aviation ZephIR lidar. Proceedings of the 15th Coherent Laser Radar Conference, Toulouse, France."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"3","DOI":"10.1175\/1520-0426(1985)002<0003:COCLMW>2.0.CO;2","article-title":"Comparison of cw-lidar-measured wind values by full conical scan, conical sector scan and two-point techniques","volume":"2","author":"Schwiesow","year":"1985","journal-title":"J. Atmos. Ocean. Tech."},{"key":"ref_35","unstructured":"(2018, February 21). Leosphere. Available online: http:\/\/www.leosphere.com."},{"key":"ref_36","unstructured":"The assumption of \u201creasonable continuity\u201d should be examined:\n\t  \n          The teeing area is protected rear and right by a thick stand of tall pine trees, so that, even in a stiff wind, you are often hitting from a pocket of comparative calm. The problem is that the trees end about halfway to the green, which is the point where any wind that happens to be around begins to affect the flight of the ball. Perhaps because this is the lowest section of the course, the further and larger problem is that the wind here swirls a lot. You can glance up at the tops of those big old pine trees to your right and note that they are blowing one way, then flick your eyes over to the green and watch the flag blowing in the exactly opposite direction. Picking the correct club and shot at this hole on anything but a dead calm day is, therefore, always something of a guessing game. (J Nicklaus and K Gorman, My Story, Random House, 1997).\n          The typical working ranges (50\u2013250 m) and Lorentzian-halfwidth range resolutions of the current ZephIR lidar are well suited to modern par 3 holes and hard-to-judge approach shots. It is common for the wind direction on some areas of the author\u2019s home course to be quite different from that of the low grim clouds overhead; for example, a prevailing breeze from the west may swirl over the Malvern Hills, forming a roll or vortex structure that creates a westwards motion near ground level. The potentially large and rapid wind variations throughout such hilly or complex terrain are of interest to turbine farm companies as well as golf broadcasters."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"1485","DOI":"10.1175\/1520-0450(1975)014<1485:TDOWSI>2.0.CO;2","article-title":"The determination of wind speeds in the boundary layer by monostatic lidar","volume":"14","author":"Eloranta","year":"1975","journal-title":"J. Appl. Meteorol."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"2524","DOI":"10.1364\/AO.27.002524","article-title":"Lidar determination of winds by aerosol inhomogeneities: Motion velocity in the planetary boundary layer","volume":"27","author":"Kolev","year":"1988","journal-title":"Appl. Opt."},{"key":"ref_39","first-page":"772","article-title":"Laser sensing of wind velocity by a correlation method","volume":"12","author":"Zuev","year":"1977","journal-title":"Izv. Atmos. Ocean. Phys."},{"key":"ref_40","unstructured":"Zuev, V.E., Samokhvalov, I.V., Matvienko, G.G., Kolev, I.N., and Parvanov, O.P. (2018, January 15). Laser Sounding of Instantaneous and Mean Speed of Wind Using Correlation Method, Available online: https:\/\/ntrs.nasa.gov\/search.jsp?R=19870000871."},{"key":"ref_41","unstructured":"Samokhvalov, I.V. (1985). Correlation Method of Laser Sounding Measurements of Wind Speed, Nauka. (In Russian)."},{"key":"ref_42","first-page":"1751","article-title":"Wavelet-based optical flow for two-component wind field estimation from single aerosol lidar data","volume":"33","author":"Mauzey","year":"2015","journal-title":"J. Atmos. Ocean. Technol."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"81","DOI":"10.1175\/JTECH-D-15-0009.1","article-title":"Optimization of the cross-correlation algorithm for two-component wind field estimation from single aerosol lidar data and comparison with Doppler lidar","volume":"33","author":"Hamada","year":"2016","journal-title":"J. Atmos. Ocean. Technol."},{"key":"ref_44","unstructured":"Smalikho\n              I.N.\n            \n          \n          On measurement of the dissipation rate of the turbulent energy with a CW Doppler lidar\n          J. Atmos. Ocean. Opt.\n          1995\n          8\n          788\n          793\n         See also: \n          \n            \n              Mikkelsen\n              T.\n            \n          \n          On mean wind and turbulence profile measurements from ground-based wind lidars: Limitations in time and space resolution with continuous wave and pulsed lidar systems\n          Proceedings of the European Wind Energy Conference & Exhibition 2009\n          Marseille, France\n          16\u201319 March 2009\n         This literature defines a probe scale \u0394z = \u03bb(f\/wlens)2, roughly ~ \u03c0 times longer than the conventional Gaussian beam parameter or Rayleigh range."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"25670","DOI":"10.1364\/OE.21.025670","article-title":"Investigation of spherical aberration effects on coherent lidar performance","volume":"21","author":"Hu","year":"2013","journal-title":"Opt. Express"}],"container-title":["Remote Sensing"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2072-4292\/10\/3\/466\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T14:57:20Z","timestamp":1760194640000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2072-4292\/10\/3\/466"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2018,3,16]]},"references-count":45,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2018,3]]}},"alternative-id":["rs10030466"],"URL":"https:\/\/doi.org\/10.3390\/rs10030466","relation":{},"ISSN":["2072-4292"],"issn-type":[{"value":"2072-4292","type":"electronic"}],"subject":[],"published":{"date-parts":[[2018,3,16]]}}}