An a Posteriori Method Based on Photo-Acoustic Cell Information to Correct for Lidar Transmitter Spectral Shift: Application to Atmospheric CO2 Differential Absorption Lidar Measurements

Abstract. The feasibility of Differential Absorption Radar (DAR) for the spaceborne remote profiling of water vapor within the cloudy boundary layer is assessed by applying a radar instrument simulator to Large Eddy Simulations (LES). Frequencies near the 183 GHz water vapor absorption line attenuate too strongly to penetrate the large vapor concentrations that are ubiquitous in the boundary layer. However it is shown that lower frequencies between 140 and 170 GHz in the water vapor absorption continuum and on the wings of the absorption line, which are attenuated less efficiently than those near the line center, still have sufficient spectral variation of gaseous attenuation to perform sounding. The high resolution LES allow for assessment of the potential uncertainty in the method due to natural variability in thermodynamic and dynamic variables on scales smaller than the instrument field of view. The (160, 170) GHz frequency pair is suggested to best maximize signal for vapor profiling while minimizing noise due to undesired spectral variation in the target extinction properties. Precision in the derived water vapor is quantified as a function of the range resolution and the instrument precision. Assuming an observational spatial scale of 500 m vertical and 750 m Full Width at Half Maximum (FWHM) horizontal, measurement precision better that 1 g m−3 is achievable for stratocumulus scenes and 3 g m−3 for cumulus scenes given precision in radar reflectivity of 0.16 dBZ. Expected precision in the Column Water Vapor (CWV) is achievable between 0.5 and 2 kg m−2 on these same spatial scales. Sampling efficiency is quantified as a function of radar sensitivity. Mean biases in CWV due to natural variability in the target extinction properties do not exceed 0.25 kg m−2. Potential biases due to uncertainty in the temperature and pressure profile are negligible relative to those resulting from natural variability. Assuming a −35 dBZ minimum detectable signal, 40 % (21.9 %) of stratocumulus (cumulus) atmospheric boundary layer range bins would be sampled. Simulated surface reflectivities are always greater than −5 dBZ, which implies the DAR technique could provide near spatially continuous observation of the CWV in subtropical boundary layers at a spatial resolution better than 1 km.

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ON-LINE WAVELENGTH CALIBRATION OF PULSED LASER FOR CO2 DIFFERENTIAL ABSORPTION LIDAR

ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences ◽

10.5194/isprsarchives-xli-b1-141-2016 ◽

2016 ◽

Vol XLI-B1 ◽

pp. 141-146

Author(s):

Chengzhi Xiang ◽

Xin Ma ◽

Ge Han ◽

Ailin Liang ◽

Wei Gong

Keyword(s):

Absorption Line ◽

Pulsed Laser ◽

Tunable Laser ◽

Differential Absorption ◽

Differential Absorption Lidar ◽

Wavelength Calibration ◽

Large Fluctuations ◽

Complete Absorption ◽

Multi Wavelength ◽

On Line

Differential absorption lidar (DIAL) remote sensing is a promising technology for atmospheric CO2 detection. However, stringent wavelength accuracy and stability are required in DIAL system. Accurate on-line wavelength calibration is a crucial procedure for retrieving atmospheric CO2 concentration using the DIAL, particularly when pulsed lasers are adopted in the system. Large fluctuations in the intensities of a pulsed laser pose a great challenge for accurate on-line wavelength calibration. In this paper, a wavelength calibration strategy based on multi-wavelength scanning (MWS) was proposed for accurate on-line wavelength calibration of a pulsed laser for CO2 detection. The MWS conducted segmented sampling across the CO2 absorption line with appropriate number of points and range of widths by using a tunable laser. Complete absorption line of CO2 can be obtained through a curve fitting. Then, the on-line wavelength can be easily found at the peak of the absorption line. Furthermore, another algorithm called the energy matching was introduced in the MWS to eliminate the backlash error of tunable lasers during the process of on-line wavelength calibration. Finally, a series of tests was conducted to elevate the calibration precision of MWS. Analysis of tests demonstrated that the MWS proposed in this paper could calibrate the on-line wavelength of pulsed laser accurately and steadily.

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The feasibility of water vapor sounding of the cloudy boundary layer using a differential absorption radar technique

Atmospheric Measurement Techniques ◽

10.5194/amt-8-3631-2015 ◽

2015 ◽

Vol 8 (9) ◽

pp. 3631-3645 ◽

Cited By ~ 13

Author(s):

M. D. Lebsock ◽

K. Suzuki ◽

L. F. Millán ◽

P. M. Kalmus

Keyword(s):

Boundary Layer ◽

Water Vapor ◽

Absorption Line ◽

Spatial Scales ◽

Natural Variability ◽

Line Center ◽

Spectral Variation ◽

Differential Absorption ◽

Water Vapor Absorption ◽

Vapor Absorption

Abstract. The feasibility of differential absorption radar (DAR) for the spaceborne remote profiling of water vapor within the cloudy boundary layer is assessed by applying a radar instrument simulator to large eddy simulations (LES). Frequencies near the 183 GHz water vapor absorption line attenuate too strongly to penetrate the large vapor concentrations that are ubiquitous in the boundary layer. However it is shown that lower frequencies between 140 and 170 GHz in the water vapor absorption continuum and on the wings of the absorption line, which are attenuated less efficiently than those near the line center, still have sufficient spectral variation of gaseous attenuation to perform sounding. The high resolution LES allow for assessment of the potential uncertainty in the method due to natural variability in thermodynamic and dynamic variables on scales smaller than the instrument field of view. The (160, 170) GHz frequency pair is suggested to best maximize signal for vapor profiling while minimizing noise due to undesired spectral variation in the target extinction properties. Precision in the derived water vapor is quantified as a function of the range resolution and the instrument precision. Assuming an observational spatial scale of 500 m vertical and 750 m full width at half maximum (FWHM) horizontal, measurement precision better that 1 g m−3 is achievable for stratocumulus scenes and 3 g m−3 for cumulus scenes given precision in radar reflectivity of 0.16 dBZ. Expected precision in the column water vapor (CWV) is achievable between 0.5 and 2 kg m−2 on these same spatial scales. Sampling efficiency is quantified as a function of radar sensitivity. Mean biases in CWV due to natural variability in the target extinction properties do not exceed 0.25 kg m−2. Potential biases due to uncertainty in the temperature and pressure profile are negligible relative to those resulting from natural variability. Assuming a −35 dBZ minimum detectable signal, 40 %(21.9 %) of stratocumulus(cumulus) atmospheric boundary layer range bins would be sampled. Simulated surface reflectivities are always greater than −5 dBZ, which implies the DAR technique could provide near spatially continuous observation of the CWV in subtropical boundary layers at a spatial resolution better than 1 km.

Download Full-text

ON-LINE WAVELENGTH CALIBRATION OF PULSED LASER FOR CO2 DIFFERENTIAL ABSORPTION LIDAR

ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences ◽

10.5194/isprs-archives-xli-b1-141-2016 ◽

2016 ◽

Vol XLI-B1 ◽

pp. 141-146

Author(s):

Chengzhi Xiang ◽

Xin Ma ◽

Ge Han ◽

Ailin Liang ◽

Wei Gong

Keyword(s):

Absorption Line ◽

Pulsed Laser ◽

Tunable Laser ◽

Differential Absorption ◽

Differential Absorption Lidar ◽

Wavelength Calibration ◽

Large Fluctuations ◽

Complete Absorption ◽

Multi Wavelength ◽

On Line

Differential absorption lidar (DIAL) remote sensing is a promising technology for atmospheric CO2 detection. However, stringent wavelength accuracy and stability are required in DIAL system. Accurate on-line wavelength calibration is a crucial procedure for retrieving atmospheric CO2 concentration using the DIAL, particularly when pulsed lasers are adopted in the system. Large fluctuations in the intensities of a pulsed laser pose a great challenge for accurate on-line wavelength calibration. In this paper, a wavelength calibration strategy based on multi-wavelength scanning (MWS) was proposed for accurate on-line wavelength calibration of a pulsed laser for CO2 detection. The MWS conducted segmented sampling across the CO2 absorption line with appropriate number of points and range of widths by using a tunable laser. Complete absorption line of CO2 can be obtained through a curve fitting. Then, the on-line wavelength can be easily found at the peak of the absorption line. Furthermore, another algorithm called the energy matching was introduced in the MWS to eliminate the backlash error of tunable lasers during the process of on-line wavelength calibration. Finally, a series of tests was conducted to elevate the calibration precision of MWS. Analysis of tests demonstrated that the MWS proposed in this paper could calibrate the on-line wavelength of pulsed laser accurately and steadily.

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Comparison of CO2 Vertical Profiles in the Lower Troposphere between 1.6 µm Differential Absorption Lidar and Aircraft Measurements Over Tsukuba

Sensors ◽

10.3390/s18114064 ◽

2018 ◽

Vol 18 (11) ◽

pp. 4064 ◽

Cited By ~ 4

Author(s):

Yasukuni Shibata ◽

Chikao Nagasawa ◽

Makoto Abo ◽

Makoto Inoue ◽

Isamu Morino ◽

...

Keyword(s):

Lower Troposphere ◽

Average Error ◽

Vertical Profiles ◽

Aircraft Measurements ◽

Mixing Ratio ◽

Average Difference ◽

Differential Absorption ◽

Differential Absorption Lidar ◽

In Situ Sensor

A 1.6 μm differential absorption Lidar (DIAL) system for measurement of vertical CO2 mixing ratio profiles has been developed. A comparison of CO2 vertical profiles measured by the DIAL system and an aircraft in situ sensor in January 2014 over the National Institute for Environmental Studies (NIES) in Tsukuba, Japan, is presented. The DIAL measurement was obtained at an altitude range of between 1.56 and 3.60 km with a vertical resolution of 236 m (below 3 km) and 590 m (above 3 km) at an average error of 1.93 ppm. An in situ sensor for cavity ring-down spectroscopy of CO2 was installed in an aircraft. CO2 mixing ratio measured by DIAL and the aircraft sensor ranged from 398.73 to 401.36 ppm and from 399.08 to 401.83 ppm, respectively, with an average difference of −0.94 ± 1.91 ppm below 3 km and −0.70 ± 1.98 ppm above 3 km between the two measurements.

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