Our understanding of the distribution of heat and water in the atmosphere still shows critical gaps on all temporal and spatial scales. This is mainly due to a lack of accurate measurements of water vapor and temperature profiles - hereafter called thermodynamic (TD) profiles - with high vertical and temporal resolution, especially in the lower troposphere. Accurate, high temporal-spatial resolution observations of TD profiles are essential for improving weather forecasting and re-analyses, for studying land-atmosphere feedback processes and for improving model parameterizations of landsurface and turbulent transport processes in the Atmospheric Boundary Layer. These observational gaps can be addressed with a new active remote sensing system in space based on the Raman lidar technique. Combining vibrational and rotational Raman backscatter signals, simultaneous measurements of water vapour and temperature profiles and a variety of derived variables are possible with unprecedented vertical and horizontal resolution, especially in the lower troposphere. This is the key concept of ATLAS, which was submitted in March 2018 to the European Space Agency in response to the Call for Earth Explorer-10 Mission Ideas in the frame of ESA EOEP. An assessment of the expected performance of the system and the specifications of the different lidar sub-systems has been performed based on the application of an analytical simulation model for space-borne Raman lidar systems. Results from the simulations and technical aspects of the proposed mission will be illustrated at the conference.
This work focuses on the statistical analysis of day and night hourly pattern of columnar aerosol properties. To that end, we use the large database of star-photometry measurements at the University of Granada station (37.16°N, 3.60°W, 680 m a.s.l; South-East of Spain) for nighttime characterization, and co-located AERONET measurements for the daytime. The aerosol properties studied are the aerosol optical depth (AOD), Angstrom parameter (α(440-870)), aerosol optical depths of fine (AODfine) and coarse mode (AODcoarse) through the Spectral Deconvolution Algorithm (SDA). Microphysical properties are calculated by inverting AOD spectra and include the effective radius (reff) and volume concentration (V) of the total size distribution, and also the effective radius of the fine mode (rfine). The initial analysis for the different air masses that reach the study area reveals that generally day and night values of AOD and α(440-870) are not different statistically. Nighttime values of AODfine, reff and rfine do however, present larger values. The influence of North African air masses is remarkable both during the day and night, with high particle loads and low values of the Angstrom parameters and also with large contribution of coarse particles as AODcoarse and reff values are almost the double than for other air masses. The analyses of day-to-night hourly values reveal an increase in AOD, AODfine and AODcoarse during the day and a decrease during the night. Such a pattern could be explained by the different emission rates, accumulation, aging and deposition of particles. Changes in particle radius are also observed as part of the day-tonight particle evolution process, being rfine variations important mainly at daytime while for reff variations are more important at nighttime. Results of day-to-night evolution were found to be independent of air mass origin, and seem to be mainly associated with local processes.
The Georgia Tech Research Institute (GTRI) is developing a transportable multi-lidar instrument known as the Integrated Atmospheric Characterization System (IACS). The system will be housed in two shipping containers that will be transported to remote sites on a low-boy trailer. IACS will comprise three lidars: a 355 nm imaging lidar for profiling refractive turbulence, a 355 nm Raman lidar for profiling water vapor, and an aerosol lidar operating at 355 nm as well as 1.064 and 1.627 µm. All of the lidar transmit/receive optics will be on a common mount, pointable at any elevation angle from 10 degrees below horizontal to vertical. The entire system will be computer controlled to facilitate pointing and automatic data acquisition. The purpose of IACS is to characterize optical propagation paths during outdoor tests of electro-optical systems. The tests are anticipated to include ground-to-ground, air-to-ground, and ground-to-air scenarios, so the system must accommodate arbitrary slant paths through the atmosphere, with maximum measurement ranges of 5-10 km. Elevation angle scans will be used to determine atmospheric extinction profiles at the infrared wavelengths, and data from the three wavelengths will be used to determine the aerosol Angstrom coefficient, enabling interpolation of results to other wavelengths in the 355 nm to 1.627 µm region.
We show here new results of a Raman LIDAR calibration methodology effort putting emphasis in the assessment
of the cross-section ratio between water vapor and nitrogen by the use of a calibrated NIST traceable tungsten
lamp. Therein we give a step by step procedure of how to employ such equipment by means of a mapping/scanning
procedure over the receiving optics of a water vapor Raman LIDAR. This methodology has been independently
used at Howard University Raman LIDAR and at IPEN Raman LIDAR what strongly supports its reproducibility
and points towards an independently calibration methodology to be carried on within an experiment routine.
The Georgia Tech Research Institute (GTRI) is developing a transportable multi-lidar instrument known as the
Integrated Atmospheric Characterization System (IACS). The system will be housed in standard shipping containers that
will be transported to remote sites by tractor-trailer. IACS will comprise three lidars: a 355 nm imaging lidar for
profiling refractive turbulence, a 355 nm Raman lidar for profiling water vapor, and an aerosol lidar operating at both
1.06 and 1.625 microns. All of the lidar transmit/receive optics will be co-aligned on a common mount, pointable at any
elevation angle from horizontal to vertical. The entire system will be computer controlled to facilitate pointing and
automatic data acquisition. The purpose of IACS is to characterize optical propagation paths during outdoor tests of
electro-optical systems. The tests are anticipated to include ground-to-ground, air-to-ground, and ground-to-air scenarios,
so the system must accommodate arbitrary slant paths through the atmosphere with maximum measurement ranges of
5-10 km. Elevation angle scans will be used to determine atmospheric extinction profiles at the infrared wavelengths, and
data from the three wavelengths will be used to determine the aerosol Angstrom coefficient, enabling interpolation of
results to other wavelengths in the 355 nm to 1.6 micron region. The imaging lidar for profiling refractive turbulence is
based on a previously-reported project known as Range Profiles of Turbulence.
The work described here reports on the improvement of a Raman lidar algorithm for measuring aerosol extinction. In order to calculate aerosol extinction from Raman lidar data it is necessary to perform the derivative of a molecular Raman signal with respect to altitude. The typical approach taken in the lidar community is to make an a priori assumption about the functional behavior of the data in order to calculate the derivative. Here a technique is shown that uses the chi-squared test to determine the most likely functional behavior of the data prior to actually calculating the derivative. A mathematical simulation is described that shows the capabilities of this technique and the possibility of reducing the extinction uncertainties with respect to traditional techniques.
Understanding upper troposphere humidity is important in the context of radiative forcing and climate. We present a detailed statistic comparison of upper troposphere water vapor retrieval profiles derived from the Atmospheric Infrared Sounder (AIRS) and in-situ measurements. The in-situ measurements are based on a recently compiled database of "best estimate" atmospheric state profiles, obtained from a careful selection of RS-90 radiosondes at Department of Energy Atmospheric Radiation Measurement (ARM) sites, during AIRS overpasses. The aim of this research is to improve the skill and accuracy of the retrieval algorithms in order to understand and quantify the biases between AIRS and RS-90 radiosondes.
Richard Ferrare, Edward Browell, Syed Ismail, Susan Kooi, Vince Brackett, Marian Clayton, Anthony Notari, Carolyn Butler, John Barrick, Glenn Diskin, Barry Lesht, Frank Schmidlin, Dave Turner, David Whiteman, Larry Miloshevich
Measurements of water vapor profiles over the Southern Great Plains acquired by two different lidars are presented. NASA's airborne DIAL Lidar Atmospheric Sensing Experiment (LASE) system measured water vapor, aerosol, and cloud profiles during the ARM/FIRE Water Vapor Experiment (AFWEX) in November-December 2000 and during the International H2O Project (IHOP) in May-June 2002. LASE measurements acquired during AFWEX are used to characterize upper troposphere water vapor measured by ground-based Raman lidars, radiosondes, and in situ aircraft sensors. LASE measurements acquired during IHOP are being used to better understand the influence water vapor variability on the initiation of deep convection and to improve the quantification and prediction of precipitation associated with these storms. The automated Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) Cloud and Radiation Testbed (CART) Raman Lidar (CARL) has been routinely measuring profiles of water vapor mixing ratio, relative humidity, aerosol extinction, aerosol backscattering, and aerosol and cloud depolarization during both daytime and nighttime operations. Aerosol and water vapor profiles acquired since March 1998 are used to investigate the seasonal variability of the vertical distributions of water vapor and aerosols.
Ground-based Atmospheric Emitted Radiance Interferometer (AERI) and
Raman Lidar measurements are used to infer cirrus cloud absorption optical depth and effective particle size. Our methodology will be discussed, and results shown for a number of contrasting cloud cases. The high spectral resolution AERI measurements allow inversion of the infrared radiative transfer equation between gaseous absorption lines (e.g., regions of minimal atmospheric emission), referred to as microwindows, to derive the cloud infrared absorption optical depth. Spectral variation in the cloud optical depth yields information on particle size and shape. A best fit of absorption optical depth to the measured absorption optical depth in each microwindow is used to determine the effective radius of particles within the cloud. Results will also be compared to simultaneous upwelling aircraft measurements.
The ARM-FIRE Water Vapor Experiment (AFWEX) was conducted during November-December 2000 at the Southern Great Plains (SGP) Cloud and Radiation Testbed (CART). A cirrus event which occurred on 7-8 December was analyzed using ground- and aircraft-based measurements. The ground-based Atmospheric Emitted Radiance Interferometer (AERI) and NPOESS Airborne Sounder Testbed-Interferometer (NAST-I) are high spectral resolution interferometers which measure downwelling and upwelling infrared radiation, respectively. Analysis between water vapor absorption lines within the 8 to 12 μm atmospheric window allow inversion of the radiative transfer equation to derive the cirrus cloud optical depth. These data will be compared to ground-based Raman lidar (GSFC and ARM) measurements of cirrus optical depth. The NAST-I measurements were conducted from the Proteus aircraft.
A new technique for measuring cloud liquid water, mean droplet radius and droplet number density has been presented elsewhere and is reviewed here. A new extension of the theory is then presented which allows multiple scattering to be quantified. The technique is based on simultaneously measuring Raman and Mie scattering from cloud liquid droplets using a Raman lidar. The intensity of Raman scattering is known to be proportional to the amount of liquid present in cloud droplets. This fact is used as a constraint on calculated Mie intensity to calculate droplet radius and number density. The technique is tested using Raman lidar data. The general relationship of retrieved average radius and number density is consistent with traditional cloud physics models.
As a part of the international Network for the Detection of Stratospheric Change, Goddard Space Flight Center has developed a mobile differential absorption lidar capable of making precise and accurate measurements in the stratosphere between 20 and 45 km. We present in this paper a description of the instrument, a discussion of the data analysis,
and some results from an intercomparison held at JPL's Table Mountain Observatory in California during October and November 1988.
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