Showing papers on "Atmospheric lidar published in 2020"

Experimental Calibration of the Overlap Factor for the Pulsed Atmospheric Lidar by Employing a Collocated Scheimpflug Lidar

Abstract: Lidar techniques have been widely employed for atmospheric remote sensing during past decades. However, an important drawback of the traditional atmospheric pulsed lidar technique is the large blind range, typically hundreds of meters, due to incomplete overlap between the transmitter and the receiver, etc. The large blind range prevents the successful retrieval of the near-ground aerosol profile, which is of great significance for both meteorological studies and environmental monitoring. In this work, we have demonstrated a new experimental approach to calibrate the overlap factor of the Mie-scattering pulsed lidar system by employing a collocated Scheimpflug lidar (SLidar) system. A calibration method of the overlap factor has been proposed and evaluated with lidar data measured in different ranges. The overlap factor, experimentally determined by the collocated SLidar system, has also been validated through horizontal comparison measurements. It has been found out that the median overlap factor evaluated by the proposed method agreed very well with the overlap factor obtained by the linear fitting approach with the assumption of homogeneous atmospheric conditions, and the discrepancy was generally less than 10%. Meanwhile, simultaneous measurements employing the SLidar system and the pulsed lidar system have been carried out to extend the measurement range of lidar techniques by gluing the lidar curves measured by the two systems. The profile of the aerosol extinction coefficient from the near surface at around 90 m up to 28 km can be well resolved in a slant measurement geometry during nighttime. This work has demonstrated a great potential of employing the SLidar technique for the calibration of the overlap factor and the extension of the measurement range for pulsed lidar techniques.

ESA’s Lidar Missions Aeolus and EarthCARE

Abstract: ESAs Earth Explorer Aeolus was launched in August 2018. Aboard the first spaceborne wind lidar ALADIN (Atmospheric LAser Doppler INstrument) was switched on in early September 2018 and demonstrated the capability to provide atmospheric wind profiles globally from particle and molecular backscatter. In doing so, it will contribute to the improvement in numerical weather prediction (NWP) and the understanding of global dynamics. At the same, it is a major step for powerful and frequency stabilized ultraviolet (UV) lasers for space applications. In parallel, ESA and its partners continue the development of this technology by setting up further ground tests based on Aeolus, and preparing the next milestone with ATLID (ATmospheric LIDar) for the Earth Cloud, Aerosol and Radiation Explorer (EarthCARE) mission. ATLID is currently fully integrated and getting prepared for its on-ground testing.

Implementation of UV rotational Raman channel to improve aerosol retrievals from multiwavelength lidar.

Abstract: Vibrational Raman effect is widely used in atmospheric lidar systems, but rotational Raman present several advantages. We have implemented a new setup in the ultraviolet branch of an existing multiwavelength lidar system to collect signal from rotational Raman lines of Oxygen and Nitrogen. We showed that, with an appropriate filter wavelength selection, the systematic error introduced in the particle optical properties due to temperature dependence was less than 4%. With this new setup, we have been able to retrieve aerosol extinction and backscatter coefficients profiles at 355 nm with 1-h time resolution during daytime and up to 1-min time resolution during nighttime.

Development of ATLID Retrieval Algorithms

Abstract: ATLID (“ATmospheric LIDar”) is the lidar to be flown on the multi-instrument Earth Clouds and Radiation Explorer (EarthCARE or ECARE) joint ESA/JAXA mission now scheduled for launch in 2022. ATID is a 3 channel linearly polarized High-Spectral Resolution (HSRL) system operating at 355nm. Cloud and aerosol optical properties are key ECARE products. This paper will provide an overview of the ATLID L2a (i.e. single instrument) retrieval algorithms being developed and implemented in order to derive cloud and aerosol optical properties.

Flight Lidar Development and Qualification for the ESA Earth Cloud Aerosol and Radiation Explorer (Earthcare) Mission

Abstract: The ATmospheric LIDAR (Light Detection and Ranging), ATLID, is part of the payload of the Earth Cloud, Aerosol and Radiation Explorer (EarthCARE) mission, the sixth Earth Explorer Mission of the European Space Agency (ESA) Living Planet Programme [1]. The EarthCARE payload consists of four instruments that will, in a synergetic manner, retrieve vertical profiles of clouds and aerosols, and the characteristics of the radiative and microphysical properties, to determine flux gradients within the atmosphere and top of atmosphere radiance and flux. ATLID's objective is to provide vertical profiles of optically thin cloud and aerosol layers, as well as the altitude of cloud boundaries. With that purpose ATLID emits <35ns duration laser pulses with 40mJ energy in the UV, at a repetition rate of 51 Hz, while pointing in a near nadir direction along track of the satellite trajectory. The backscatter signal is collected by a 620 mm aperture telescope and is then filtered and redirected through the optics of the instrument focal plane assembly, in such a way that, the atmospheric Mie and Rayleigh scattering contributions are separated and independently measured. After the full instrument assembly completion, ATLID has been initially subjected to an ambient performance tests campaign, followed by a complete environmental qualification test campaign including performance calibration and characterization in thermal vacuum conditions in order to approximate the on-orbit operational conditions. Whilst the full set of test data is currently being processed, early analysis of preliminary test results indicates that the instrument is fully compliant with expected performance. In this paper the design of ATLID is recalled and major instrument manufacturing, assembly and testing steps are presented. It is foreseen that the calibration and qualification test result shall be confirmed and presented at the time of the conference.

Adaptive digital filter for the processing of atmospheric lidar signals measured by imaging lidar techniques.

Abstract: The lidar signal measured by the atmospheric imaging lidar technique is subject to sunlight background noise, dark current noise, and fixed pattern noise (FPN) of the image sensor, etc., which presents quite different characteristics compared to the lidar signal measured by the pulsed lidar technique based on the time-of-flight principle. Enhancing the signal-to-noise ratio (SNR) of the measured lidar signal is of great importance for improving the performance of imaging lidar techniques. By carefully investigating the signal and noise characteristics of the lidar signal measured by a Scheimpflug lidar (SLidar) based on the Scheimpflug imaging principle, we have demonstrated an adaptive digital filter based on the Savitzky–Golay (S–G) filter and the Fourier analysis. The window length of the polynomial of the S–G filter is automatically optimized by iteratively examining the Fourier domain frequency characteristics of the residual signal between the filtered lidar signal and the raw lidar signal. The performance of the adaptive digital filter has been carefully investigated for lidar signals measured by a SLidar system under various atmospheric conditions. It has been found that the optimal window length for near horizontal measurements is concentrated in the region of 90–150, while it varies mainly in the region of 40–100 for slant measurements due to the frequent presence of the peak echoes from clouds, aerosol layers, etc. The promising result has demonstrated great potential for utilizing the proposed adaptive digital filter for the lidar signal processing of imaging lidar techniques in the future.

Low-Swap Elastic Backscatter Lidar for Close-Range Aerosol Detection

Abstract: A small form-factor atmospheric lidar demonstrator was developed for high resolution measurements of aerosols. The system is a conventional elastic backscatter lidar with a pulsed laser transmitter operating at a wavelength 1.54 µm coupled with a 2-inch diameter receiver. The intended purpose of the lidar system is to detect various aerosols in the atmosphere at high spatio-temporal resolution and close observational range. The intentionally low Size, Weight and Power (SWaP) of the system design enables use on a variety of fixed and airborne platforms (i.e. unmanned aerial systems). The relative low cost to build and operate the system facilitates proliferation of networks of such systems for increased monitoring coverage. First results from the system that show aerosol transport over a localized urban area will be presented. Future enhancements, such as a depolarization capability, will also be discussed.