Comments on “Accuracy of Raman lidar water vapor calibration and its applicability to long-term measurements”

Whiteman, David N.; Venable, D. D.; Landulfo, Eduardo

doi:10.1364/ao.50.002170

Cited by 36 publications

(26 citation statements)

References 18 publications

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“…Figure 3 shows pictures of beam spot samples that we observed at the output of our 1 mm diameter fiber for various positions and tilts of the injected light beam (from a 468 nm LED with matched numerical apertures of NA in = 0.22). Similar changes in the output beam diameter have been reported by Whiteman et al (2011). In addition to the changes in size and shape of the output beam, we also observed that the NA of the emerging beam can be larger than specified by the manufacturer.…”

Section: System (Gnss) Measurementssupporting

confidence: 88%

Study and mitigation of calibration factor instabilities in a water vapor Raman lidar

et al. 2017

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Abstract. We have investigated calibration variations in the Rameau water vapor Raman lidar. This lidar system was developed by the Institut National de l'Information Géo-graphique et Forestière (IGN) together with the Laboratoire Atmosphères, Milieux, Observations Spatiales (LAT-MOS). It aims at calibrating Global Navigation Satellite System (GNSS) measurements for tropospheric wet delays and sounding the water vapor variability in the lower troposphere. The Rameau system demonstrated good capacity in retrieving water vapor mixing ratio (WVMR) profiles accurately in several campaigns. However, systematic shortterm and long-term variations in the lidar calibration factor pointed to persistent instabilities. A careful testing of each subsystem independently revealed that these instabilities are mainly induced by mode fluctuations in the optic fiber used to couple the telescope to the detection subsystem and by the spatial nonuniformity of the photomultiplier photocathodes. Laboratory tests that replicate and quantify these instability sources are presented. A redesign of the detection subsystem is presented, which, combined with careful alignment procedures, is shown to significantly reduce the instabilities. Outdoor measurements were performed over a period of 5 months to check the stability of the modified lidar system. The calibration changes in the detection subsystem were monitored with lidar profile measurements using a common nitrogen filter in both Raman channels. A short-term stability of 2-3 % and a long-term drift of 2-3 % per month are demonstrated. Compared to the earlier Development of Methodologies for Water Vapour Measurement (DEMEVAP) campaign, this is a 3-fold improvement in the long-term stability of the detection subsystem. The overall water vapor calibration factors were determined and monitored with capacitive humidity sensor measurements and with GPS zenith wet delay (ZWD) data. The changes in the water vapor calibration factors are shown to be fairly consistent with the changes in the nitrogen calibration factors. The nitrogen calibration results can be used to correct the overall calibration factors without the need for additional water vapor measurements to within 1 % per month.

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Section: System (Gnss) Measurementssupporting

confidence: 88%

Study and mitigation of calibration factor instabilities in a water vapor Raman lidar

et al. 2017

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“…Various approaches have been tested to calibrate the water vapour measurements of a Raman lidar system. However, calibration issues are still pending and debated (Whiteman et al, 2011a;. Though an absolute calibration of the entire lidar system is theoretically possible (Vaughan et al, 1988;Sherlock et al, 1999b;Venable et al, 2011), the signal ratio is usually scaled to various external water vapour measurements (radiosonde, microwave radiometer, Global Positioning System (GPS),.…”

Section: Water Vapour Mixing Ratiomentioning

confidence: 99%

A Raman lidar at La Reunion (20.8° S, 55.5° E) for monitoring water vapour and cirrus distributions in the subtropical upper troposphere: preliminary analyses and description of a future system

et al. 2012

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Abstract.A ground-based Rayleigh lidar has provided continuous observations of tropospheric water vapour profiles and cirrus cloud using a preliminary Raman channels setup on an existing Rayleigh lidar above La Reunion over the period [2002][2003][2004][2005]. With this instrument, we performed a first measurement campaign of 350 independent water vapour profiles. A statistical study of the distribution of water vapour profiles is presented and some investigations concerning the calibration are discussed. Analysis regarding the cirrus clouds is presented and a classification has been performed showing 3 distinct classes. Based on these results, the characteristics and the design of a future lidar system, to be implemented at the new Reunion Island altitude observatory (2200 m) for long-term monitoring, is presented and numerical simulations of system performance have been realised to compare both instruments.

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“…In particular, for the MAIDO RMR-H 2 O lidar two methods are used: the calibration lamp (CL), and the passive daytime observations (PDOs). As highlighted by the works of Leblanc and McDermid (2008) and of Whiteman et al (2011a) for CL and by the work of Hoareau et al (2009) for PDOs, these methods cannot be used to provide an accurate quantification of the system optical efficiency, but only to identify ISPs.…”

Section: System Monitoring: Calibration Lamp and Passive Daytime Obsementioning

confidence: 99%

Water vapor observations up to the lower stratosphere through the Raman lidar during the Maïdo Lidar Calibration Campaign

et al. 2015

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Abstract.A new lidar system devoted to tropospheric and lower stratospheric water vapor measurements has been installed at the Maïdo altitude station facility of Réunion island, in the southern subtropics.To evaluate the performances and the capabilities of the new system with a particular focus on UTLS (Upper Troposphere Lower Stratosphere) measurements, the Maïdo Lidar Calibration Campaign (MALICCA) was performed in April 2013.Varying the characteristics of the transmitter and the receiver components, different system configuration scenarios were tested and possible parasite signals (fluorescent contamination, rejection) were investigated. A hybrid calibration methodology has been set up and validated to insure optimal lidar calibration stability with time. In particular, the receiver transmittance is monitored through the calibration lamp method that, at the moment, can detect transmittance variations greater than 10-15 %. Calibration coefficients are then calculated through the hourly values of IWV (Integrated Water Vapor) provided by the co-located GPS. The comparison between the constants derived by GPS and Vaisala RS92 radiosondes launched at Maïdo during MALICCA, points out an acceptable agreement in terms of accuracy of the mean calibration value (with a difference of approximately 2-3 %), but a significant difference in terms of variability (14 % vs. 7-9 %, for GPS and RS92 calibration procedures, respectively).We obtained a relatively good agreement between the lidar measurements and 15 co-located and simultaneous RS92 radiosondes. A relative difference below 10 % is measured in the low and middle troposphere (2-10 km). The upper troposphere (up to 15 km) is characterized by a larger spread (approximately 20 %), because of the increasing distance between the two sensors.To measure water vapor in the UTLS region, nighttime and monthly water vapor profiles are presented and compared. The good agreement between the lidar monthly profile and the mean WVMR profile measured by satellite MLS (Microwave Limb Sounder) has been used as a quality control procedure of the lidar product, attesting the absence of significant wet biases and validating the calibration procedure.Due to its performance and location, the MAIDO H 2 O lidar will become a reference instrument in the southern subtropics, insuring the long-term survey of the vertical distribution of water vapor. Furthermore, this system allows the investigation of several scientific themes, such as stratospheretroposphere exchange, tropospheric dynamics in the subtropics, and links between cirrus clouds and water vapor.

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Comments on “Accuracy of Raman lidar water vapor calibration and its applicability to long-term measurements”

Cited by 36 publications

References 18 publications

Study and mitigation of calibration factor instabilities in a water vapor Raman lidar

Study and mitigation of calibration factor instabilities in a water vapor Raman lidar

A Raman lidar at La Reunion (20.8° S, 55.5° E) for monitoring water vapour and cirrus distributions in the subtropical upper troposphere: preliminary analyses and description of a future system

Water vapor observations up to the lower stratosphere through the Raman lidar during the Maïdo Lidar Calibration Campaign

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