Iodine Absorption Filter Research Articles

Evaluation of the Tenti S6 model for hydrocarbon fuels at elevated temperatures using filtered Rayleigh scattering measurements.

This Letter targets the assessment of the well-known Tenti S6 model for predicting the Rayleigh-Brillouin scattering (RBS) spectra of select gas-phase hydrocarbon fuels (CH4, C2H2, C2H4, C3H8, and C4H10) over a temperature range of 300 to 700 K. The Tenti S6 model is evaluated by comparing filtered Rayleigh scattering (FRS) measurements to synthetic FRS signals generated from the combination of the Tenti S6 output and an accurate iodine absorption filter model. The experimental and synthetic FRS results agree very well (<3% difference) over the full temperature range for CH4, C2H2, and C2H4, indicating accurate calculation of the RBS spectra. For C3H8 and C4H10, there are some large differences between the experimental and synthetic FRS results which cannot be resolved through tuning of bulk viscosity, internal heat capacity, or inclusion of vibrational degrees of freedom, suggesting the need for detailed measurements of the Rayleigh-Brillouin spectra.

Dual-Wavelength High-Spectral-Resolution Lidar for Profiling Optical Properties of Aerosol and Cloud

A dual-wavelength high-spectral-resolution lidar (HSRL) based on an iodine absorption filter and a field-widened Michelson interferometer (FWMI) has been developed to profile backscatter and extinction coefficients of aerosols and clouds accurately. This instrument was tested and calibrated on multiple observations in Hangzhou and Zhoushan, respectively, from August 2018 to April 2019. This paper discusses the design and the internal calibration method of the lidar system in detail, with several typical cases of observations and the analysis of these data products. The optical properties of urban aerosols in Hangzhou and the evolvement of clouds in Zhoushan are presented, respectively.

Performance estimation of space-borne high-spectral-resolution lidar for cloud and aerosol optical properties at 532 nm.

Cloud and aerosol contribute with great uncertainty in Earth's radiative budget. There is an urgent need for global 3-D observation of these atmospheric constituents. High-spectral-resolution Lidar (HSRL) can obtain vertical atmosphere profile with high accuracy, hence several space-borne HSRLs are planned to launch in few years. However, as far as we know, the performance evaluation of space-borne HSRL has not been reported yet. In this paper, we present the characteristics of a new designed space-borne HSRL for aerosol and cloud optical property profiling (ACHSRL), which is part of the Aerosol & Carbon Detection Lidar (ACDL) developed in China. The ACHSRL is essentially similar to the famous Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP), which is on board the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO). Moreover, the ACHSRL employs an iodine absorption filter as the spectral discriminator. The atmospheric optical properties data observed by CALIOP is used to estimate the performance of ACHSRL. We chose the level 2 profile data (version 4.10) in South Japan in June 2015 to compare the detection uncertainty of ACHSRL and CALIOP. The simulation calculates the uncertainties of ACHSRL and makes a statistic analysis. The analysis result demonstrates that 73.63% of the backscatter coefficient uncertainties are below 40% for ACHSRL. By contrast, the number is 30.72% for CALIOP. As for absolute extinction coefficient errors, the statistics shows that 76.01% of the extinction coefficient uncertainties are lower than 0.2 km-1 for ACHSRL, while that for CALIOP are 56.97%. The assessment shows that ACHSRL could measure the particulate optical properties with better accuracy and compared with CALIOP. The estimation in this study reveals that the next generation space-borne HSRLs have a promising future.

高光谱分辨率激光雷达探测大气透过率

A high spectral resolution lidar(HSRL) based on injection-seeded laser and iodine absorption filter has been developed. The basic principle, data processing method and configuration of HSRL were introduced. The HSRL measurement of atmospheric transmission in cloud and dust cases were presented,and compared with the results retrieved by the traditional Fernald method. Due to the nonidentity in physical and optical properties of different aerosols and cloud, the lidar ratio assumed in Fernald method cannot agrees well with the real atmosphere and produces considerable error in atmospheric transmission. Utilizing different spectral width of molecular scattering and particle scattering, the HSRL could separate two kinds of signals with iodine filter. Therefore, HSRL can measure the atmospheric transmission quantitatively without the additional assumption of lidar ratio.

Development of High Spectral Resolution Lidar System for Measuring Aerosol and Cloud

A high spectral resolution lidar (HSRL) system based on injection-seeded Nd:YAG laser and iodine absorption filter has been developed for the quantitative measurement of aerosol and cloud. The laser frequency is stabilized at 80 MHz by a frequency locking system and the absorption line of iodine cell is selected at the 1111 line with 2 GHz width. The observations show that the HSRL can provide vertical profiles of particle extinction coefficient, backscattering coefficient and lidar ratio for cloud and aerosol up to 12 km altitude, simultaneously. For the measured cases, the lidar ratios are 10~20 sr for cloud, 28~37 sr for dust, and 58~70 sr for urban pollution aerosol. It reveals the potential of HSRL to distinguish the type of aerosol and cloud. Time series measurements are given and demonstrate that the HSRL has ability to continuously observe the aerosol and cloud for day and night.

Airborne high spectral resolution lidar for measuring aerosol extinction and backscatter coefficients

An airborne high spectral resolution lidar (HSRL) based on an iodine absorption filter and a high-power frequency-doubled Nd:YAG laser has been developed to measure backscatter and extinction coefficients of aerosols and clouds. The instrument was operated aboard the Falcon 20 research aircraft of the German Aerospace Center (DLR) during the Saharan Mineral Dust Experiment in May-June 2006 to measure optical properties of Saharan dust. A detailed description of the lidar system, the analysis of its data products, and measurements of backscatter and extinction coefficients of Saharan dust are presented. The system errors are discussed and airborne HSRL results are compared to ground-based Raman lidar and sunphotometer measurements.

Single camera three component planar velocity measurements using two-frequency planar Doppler velocimetry (2ν-PDV)

Two-frequency planar Doppler velocimetry (2ν-PDV) is used in conjunction with imaging fibre bundles to make time-averaged three component velocity measurements using a single CCD camera and iodine cell. In this scheme the flow is sequentially illuminated with two different frequencies of laser light, which are separated by approximately 700 MHz to 1 GHz. Images are captured for each illumination frequency on a CCD camera viewing through an iodine absorption filter. These images are then used to produce a normalized transmission image that can be processed as in normal PDV. Three component measurements are made possible by porting separate views to a single CCD camera using the imaging fibre bundles. Results are presented here for a 2ν-PDV system demonstrated making time-averaged velocity measurements on a rotating disc and a seeded air jet.

High-spectral-resolution lidar using an iodine absorption filter for atmospheric measurements

We develop high-spectral-resolution lidar (HSRL) using an io- dine absorption filter and a narrow-band Nd:YAG laser with high- frequency-doubled output and use it for atmospheric measurements at the National Institute for Environmental Studies (NIES). The lidar system separates Doppler-broadened molecular scattering and unbroadened aerosol scattering components of the backscattered laser light, conse- quently providing direct measurements of these two signals. Due to stable and strong absorption at room temperature, iodine absorption fil- ters are easy to use and they enable high rejection against aerosol scat- tering with a short length. The measurement principle with an error analysis and the system construction of the HSRL are described. Ex- amples of aerosol and cloud observations made by the HSRL are also presented. The experimental results indicate that the HSRL is a powerful tool for quantitatively measuring aerosol and cloud optical properties. The use of a high-output laser gives our system the ability to provide stratospheric observations. We also present the HSRL measurements of the stratospheric temperature and backscatter profiles with better reso- lutions in both range and time. An example of temperature and backscat- ter measurements is shown for the altitude range from ;10 to ;40 km with a vertical resolution of 300 m and an integrated time of ; 2h . © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)00910-1)

Iodine absorption filters for Doppler global velocimetry

The iodine absorption filter is a critical component in the implementation of the emerging flow measurement technique of Doppler global velocimetry. The aim of this paper is to discuss the various factors influencing the performance of this type of frequency sensitive optical filter and to suggest how its design should be optimized. This advice, based upon the authors' own experience and a surprisingly large body of literature, is designed to help prospective users of Doppler global velocimetry. Some of the material may also have relevance to other forms of optical measurement which employ absorption filters.

Demonstration of a high-spectral-resolution lidar based on an iodine absorption filter

A high-spectral-resolution lidar that uses an iodine absorption filter and a tunable, narrow-bandwidth Nd:YAG laser is demonstrated. Measurements of aerosol scattering cross section and optical depth are presented. The iodine absorption filter provides better performance than the Fabry–Perot etalon that it replaces.