A recent laboratory study suggests that water vapor displays structured absorption features over the 290–350 nm region, with maximum and minimum cross‐sections of 8.4 × 10−25and 1.4 × 10−25 cm2/molecule at room temperature (Pei et al. 2019,
This work presents the first demonstration of atmospheric temperature measurement using the differential absorption lidar (DIAL) technique. While DIAL is routinely used to measure atmospheric gases such as ozone and water vapor, almost no success has been found in using DIAL to measure atmospheric temperature. Attempts to measure temperature using a well-mixed gas like oxygen (
- PAR ID:
- 10128444
- Publisher / Repository:
- Optical Society of America
- Date Published:
- Journal Name:
- Optics Express
- Volume:
- 28
- Issue:
- 1
- ISSN:
- 1094-4087; OPEXFF
- Format(s):
- Medium: X Size: Article No. 71
- Size(s):
- Article No. 71
- Sponsoring Org:
- National Science Foundation
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Abstract https://doi.org/10.1029/2019jd030724 ; Du et al., 2013,https://doi.org/10.1002/grl.50935 ). To observe water vapor absorption features in the ultraviolet (UV) region in the atmosphere, a United States Department of Agriculture reference spectroradiometer was upgraded with a new fore‐optical module, enabling it to measure direct solar beam and sky radiance at given azimuth and elevation angles. This double Czerny‐Turner spectroradiometer enables wavelength scanning from 290 to 410 nm, with a nominal bandwidth of 0.1 nm. It can operate with a step‐size of 0.0005 nm and a full width at half maximum of 0.1 nm. It has an out‐of‐band rejection ratio of approximately 10−10. This high resolution spectroradiometer can be used as a reference instrument for UV radiation measurements and for monitoring atmospheric gases such as O3, SO2, and NO2. A series of field observations were made using this spectroradiometer in the University at Albany campus. A residual analysis method is developed to analyze absorption by atmospheric components and to retrieve atmospheric optical depth. The residual optical depth was calculated by subtracting the optical depths of Rayleigh scattering, aerosol extinction, and absorption of typical atmospheric gases such as O3, SO2, and NO2from the retrieved total optical depth. Multiple case studies show that residual optical depth from the observed UV spectra is sensitive to the atmospheric water vapor amount. The greater the water vapor path, the larger the magnitude of residual optical depth. The ozone amount was inferred from the residual analysis; it is comparable to the satellite measurements. For example, in a case with water vapor path of 13 mm on October 24, 2019, the inferred ozone amount from residual analysis is 2.7% lower than retrievals from the Ozone Monitoring Instrument‐Total Ozone Mapping Spectrometer. -
Traditionally, quantitative lidar techniques like differential absorption lidar (DIAL) and high-spectral-resolution lidar (HSRL) utilize high-power-aperture product designs, which partially compensates for the need to take discrete deriva-tives of noisy data in post-processing (for number density for DIAL and extinction for HSRL) and provides for high-performance measurements, i.e., higher resolu-tion, accuracy, or precision. Conversely, low-power-aperture product lidar designs are easier to make eye-safe, reliable, and cost-effective, which are important attributes for network development and field deployment. The atmospheric science community has expressed the need for high-quality, quantitative, robust, network deployable, and cost-effective sensors for a variety of applications such as improved numerical weather forecasting – in essence requiring the best of both worlds without the accompanying drawbacks. In response to this need, the National Center for Atmospheric Research and Montana State University have been developing the MicroPulse DIAL (MPD) architecture for thermodynamic profiling in the lower atmosphere. The MPD architecture takes advantage of the benefits of low-power, low-cost laser diodes, and fiber optics to achieve quantitative profiling leverag-ing narrowband filtering and efficient elastic scattering. A field-deployable MPD instrument capable of humidity, quantitative aerosol, and temperature profiling has recently been developed. This presentation will describe the current status of this thermodynamic profiler and the initial results from a recent field deployment. Emphasis will be given to the analysis of the temperature data including compar-isons to co-located radiosondes to describe current performance.more » « less
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We demonstrate thermodynamic profile estimation with data obtained using the MicroPulse DIAL such that the retrieval is entirely self contained. The only external input is surface meteorological variables obtained from a weather station installed on the instrument. The estimator provides products of temperature, absolute humidity and backscatter ratio such that cross dependencies between the lidar data products and raw observations are accounted for and the final products are self consistent. The method described here is applied to a combined oxygen DIAL, potassium HSRL, water vapor DIAL system operating at two pairs of wavelengths (nominally centered at 770 and 828 nm). We perform regularized maximum likelihood estimation through the Poisson Total Variation technique to suppress noise and improve the range of the observations. A comparison to 119 radiosondes indicates that this new processing method produces improved temperature retrievals, reducing total errors to less than 2 K below 3 km altitude and extending the maximum altitude of temperature retrievals to 5 km with less than 3 K error. The results of this work definitively demonstrates the potential for measuring temperature through the oxygen DIAL technique and furthermore that this can be accomplished with low-power semiconductor-based lidar sensors.
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Abstract. The micropulse differential absorption lidar (MPD) was developed at Montana State University (MSU) and the National Center for Atmospheric Research (NCAR) to perform range-resolved water vapor (WV) measurements using low-power lasers and photon-counting detectors. The MPD has proven to produce accurate WV measurements up to 6 km altitude. However, the MPD's ability to produce accurate higher-altitude WV measurements is impeded by the current standard differential absorption lidar (DIAL) retrieval methods. These methods are built upon a fundamental methodology that algebraically solves for the WV using the MPD forward models and noisy observations, which exacerbates any random noise in the lidar observations. The work in this paper introduces the adapted Poisson total variation (PTV) specifically for the MPD instrument. PTV was originally developed for a ground-based high spectral resolution lidar, and this paper reports on the adaptations that were required in order to apply PTV on MPD WV observations. The adapted PTV method, coined PTV-MPD, extends the maximum altitude of the MPD from 6 to 8 km and substantially increases the accuracy of the WV retrievals starting above 2 km. PTV-MPD achieves the improvement by simultaneously denoising the MPD noisy observations and inferring the WV by separating the random noise from the non-random WV. An analysis with 130 radiosonde (RS) comparisons shows that the relative root-mean-square difference (RRMSE) of WV measurements between RS and PTV-MPD exceeds 100 % between 6 and 8 km, whereas the RRMSE between RS and the standard method exceeds 100 % near 3 km. In addition, we show that by employing PTV-MPD, the MPD is able to extend its useful range of WV estimates beyond that of the ARM Southern Great Plains Raman lidar (RRMSE exceeding 100 % between 3 and 4 km); the Raman lidar has a power-aperture product 500 times greater than that of the MPD.more » « less
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Abstract We investigate the effect of uncertainty in water vapor continuum absorption at terrestrial wavenumbers on CO2forcing , longwave feedback
λ , and climate sensitivity at surface temperaturesT sbetween 270 and 330 K. We calculate this uncertainty using a line‐by‐line radiative‐transfer model and a single‐column atmospheric model, assuming a moist‐adiabatic temperature lapse‐rate and 80% relative humidity in the troposphere, an isothermal stratosphere, and clear skies. Due to the lack of a comprehensive model of continuum uncertainty, we represent continuum uncertainty in two different idealized approaches: In the first, we assume that the total continuum absorption is constrained at reference conditions; in the second, we assume that the total continuum absorption is constrained for all atmospheres in our model. In both approaches, we decrease the self continuum by 10% and adjust the foreign continuum accordingly. We find that continuum uncertainty mainly affects through its effect onλ . In the first approach, continuum uncertainty mainly affectsλ through a decrease in the total continuum absorption withT s; in the second approach, continuum uncertainty affectsλ through a vertical redistribution of continuum absorption. In both experiments, the effect of continuum uncertainty on is modest atT s = 288 K (≈0.02 K) but substantial atT s ≥ 300 K (up to 0.2 K), because at highT s, the effects of decreasing the self continuum and increasing the foreign continuum have the same sign. These results highlight the importance of a correct partitioning between self and foreign continuum to accurately determine the temperature dependence of Earth's climate sensitivity.
