Atmospheric Transmittance Measurements Research Articles

LiDAR technology and experimental research for comprehensive measurement of atmospheric transmittance, turbulence, and wind

LiDAR technology and experimental research for comprehensive measurement of atmospheric transmittance, turbulence, and wind

从多波段图像中获取大气透过率的测量方法

从多波段图像中获取大气透过率的测量方法

大气透过率的多点移动测量

大气透过率的多点移动测量

The amplitude of the CO2 seasonal cycle in the atmosphere of the Ural region retrieved from ground-based and satellite near-IR measurements

A series of ground-based high-resolution Fourier-transform measurements of atmospheric transmittance in the near infrared region (4000–10000 cm−1) recorded at the Ural Atmospheric Station in 2012–2013 was processed in order to retrieve relative concentrations of CO2 and CH4 in the atmospheric column. Retrieved values of methane concentration do not show a noticeable seasonal cycle, while retrieved CO2 concentrations show clear seasonal variations with high amplitude, which are also observed in GOSAT measurements over the Ural region. The estimated amplitude of CO2 seasonal variations is 14–15 ppm. The comparison between CO2 ground-based and GOSAT measurements shows a good agreement, while satellite values are overestimated by approximately 3 ppm. There is no noticeable correlation between CH4 values, which could be explained by the presence of local methane sources in the area of GOSAT observations.

A Simple Method to Retrieve Cloud Properties from Atmospheric Transmittance and Liquid Water Column Measurements

Abstract A deeper knowledge of the effects and interactions of clouds in the climatic system requires developing both satellite and ground-based methods to assess their optical properties. A simple method based on a parameterized inversion of a radiative transfer model is proposed to estimate the optical depth of thick liquid water clouds from the atmospheric transmittance at 415 nm, solar zenith angle, surface albedo, effective droplet radius, and aerosol load. When concurrent measurements of atmospheric transmittance and liquid water path are available, the effective radius of the droplet size distribution can also be retrieved. The method is compared with a reference algorithm from Min and Harrison, which uses similar data, except aerosol load. When applied to measurements performed at the Southern Great Plains site of the Atmospheric Radiation Measurement Program, the mean bias deviation between the proposed method and the reference method is only −0.08 in units of optical depth, whereas the standard deviation is only 0.46. For the effective droplet radius estimations, the mean bias deviation is −0.13 μm, and the standard deviation is 0.14 μm. Maximum relative deviations are lower than 5% and 8% for cloud optical depth and effective radius, respectively. The effects on these retrievals of the assumed aerosol optical depth and surface albedo are also analyzed.

On-Orbit Calibration of the EO-1 Hyperion and Advanced Land Imager (ALI) Sensors Using the LED Spectrometer (LSpec) Automated Facility

Vicarious calibration (VC) technology, developed in the mid-1980s, has been employed to establish the absolute radiometric calibration of Earth-viewing sensors aboard satellites and aircraft. This method has heretofore required special visits by a field team to collect surface and atmospheric measurements, at specific times necessarily coincident with a sensor overflight. With the recent creation of an autonomous calibration facility, VC data can now be made available to the sensor community without the need for each research group to deploy its own field team. Beginning in mid-November 2006, there have been ongoing efforts to expand the data processing capabilities of the Jet Propulsion Laboratory-operated LED Spectrometer (LSpec) automatic facility, which has been making continual measurements of surface reflectances and atmospheric transmittances since that time. The facility is located at Frenchman Flat, within the Nevada Test Site. Data are used to support the VC of sensors which make observations at visible and near-infrared wavelengths. An array of eight LSpecs performs the autonomous function of recording surface reflectances at 5-min intervals, thereby permitting accurate and continual real-time adjustments to high-resolution Analytical Spectral Devices spectrometer measurements, acquired every several months during on-site visits. Moreover, resident at the LSpec site is a Cimel sunphotometer, used to make atmospheric transmittance measurements. The Cimel is part of the Aerosol Robotic Network (AERONET). Measurements made by the LSpec Cimel are used by AERONET to derive values of aerosol optical depths. From continuous in situ measurement of spectral reflectance of the playa surface, along with acquired aerosol optical depths and ozone optical depths (obtained from the Ozone Mapping Instrument), an LSpec database is being produced and is available via a web-based interface. To highlight the viability of making use of LSpec-derived data, we have executed a few distinct multiple scattering radiative transfer codes in order to perform VCs of the Earth Observing-1 (EO-1) Hyperion and EO-1 Advanced Land Imager sensors.

Solar‐reflectance‐based calibration of spectral radiometers

A method by which to calibrate a spectral radiometer using the sun as the illumination source is discussed. The procedure is simple, requiring only a calibrated reflectance panel, relatively low aerosol optical depth, and accurate measurements of atmospheric transmittance. Solar‐based calibrations eliminate several uncertainties associated with applying a lamp‐based calibration to field measurements and may be performed with a comparable uncertainty. A solar‐reflectance‐based calibration (SRBC), by removing the need for extraterrestrial irradiance spectra, further reduces calibration uncertainty to approximately 2.2%. This calibration may be applied to radiometric measurements of any system illuminated by the sun, such as the atmosphere or ocean, with associated reduction of uncertainty in properties derived from such measurements (e.g., aerosol single_scattering albedo). The procedure is ideal for on_site calibration of long_term field instruments, mitigating the logistics and costs associated with transport to a calibration facility.

A technique for active measurement of atmospheric transmittance using an imaging system: implementation at 10.6 μm wavelength

An active method is presented for measuring atmospheric transmittance with an imaging system. In comparison to other measurement methods, this method has the advantage of immunity to background noise, independence of atmospheric conditions such as solar radiation, and an improved capability to evaluate effects of turbulence on the measurements. Other significant advantages are integration over all particulate size distribution effects including very small and very large particulates whose concentration is hard to measure, and the fact that this method is a path-integrated measurement. Attenuation deriving from molecular absorption and from small and large particulate scatter and absorption and their weather dependences are separated out. Preliminary results indicate high correlation with direct transmittance calculations via particle size distribution measurement, and that even at 10.6 μm wavelength atmospheric transmission depends noticeably on aerosol size distribution and concentration.

Atmospheric transmittance measurements of Nd:YAG, iodine and CO 2 laser radiation over 8.6 km, and statistical analysis of extinction coefficients

A long-range multiwavelength laser transmissometer for measuring atmospheric extinction of iodine laser radiation (1.315 μm), simultaneously with Nd:YAG (1.06 μm) and CO 2 (10.6 μm) laser radiation was designed, built and operated under different atmospheric conditions, over a distance of 8.6 km in hilly terrain near Tübingen, Germany. Beam extinction was obtained by measuring the ratio of the total laser radiation to the total received radiation as collected by a mirror and focused onto a pyroelectrical detector array. Measured values of laser extinction were compared with model predictions (FASCODE 3P) based on simultaneously measured meteorological data as model input parameters. The agreement was found to be very good. It is shown that the atmospheric extinction coefficient of iodine laser radiation can be predicted to a good approximation by a linear equation containing the extinction coefficients of Nd:YAG and CO 2 laser radiation. Statistical analyses of atmospheric laser extinction coefficients are presented for these laser wavelengths. Scatter diagrams of extinction coefficients are presented for the summer and winter season together with an analysis of the annual variability. The iodine laser, if compared to the CO 2 laser, shows advantage in molecular extinction which is, however, overcompensated by aerosol extinction being often more than two orders of magnitude larger for iodine laser than for CO 2 laser radiation.

Simple Radiometer for Long-Term Monitoring of Atmospheric Transmittance in the Far IR

Generally, in the far IR (300-3000,?m), measurements of atmospheric transmittance are made with rather sophisticated instruments using liquid helium. These are not suitable for long-term monitoring of the atmosphere. In this short paper, a simple radiometer able to measure atmospheric transmittance in the 7-10-cm-1 window, is described and preliminary results are presented.

Measurements of atmospheric transmittance in the 7–10 cm−1 window at tropical observatories

Measurements of atmospheric transmittance in the 7–10 cm−1 window were made for a period of 1 month, in the dry season (observation time about 300 h.) from the F. Duarte Observatory (3,600 m. above sea level) and from experimental station of Pico Espejo (4,765 m. above sea level). Correlation with the vertical water vapor density profile have been made.

Atmospheric Noise in the Far Infrared (300-3000 /spl mu/m)

Noise measurements in the frequency regions 5-200 HZ and 5.2 x 10/sup -4/ -8.3 x 10/sup -3/ Hz have been performed in the wavelength region between 300 and 3000 mu m from the high altitude observatory of Tests Grigia, Italy (3.500 m). In the high frequency region a specially designed Ge bolometer operating in background-limited-infrared-photoconductor conditions matched to a 1.5-m telescope has been used, while at low frequency a radiometer designed for atmospheric transmittance measurements was employed. In both regions no excess noise with respect to the photon noise relative to 300-K blackbody has been detected.

Satellite Observations of Atmospheric Water Vapor

Observations in the spectral window at 11-12 microm, in the carbon dioxide band at 13.3-13.4 microm, and in the water vapor rotation band at 18.7-18.8 microm have been made by the satellite infrared spectrometer and the vertical temperature profile radiometer on the Nimbus 4 and NOAA-2 satellites. Combinations of radiances measured by the separate instruments have been used to infer sea-surface temperatures and mesoscale precipitable water in tropical regions. In each spectral interval, atmospheric transmittances for these analyses were constructed from continuous absorption (of unexplained origin), which is dependent upon the square of the partial pressure of water vapor and about the inverse fifth power of temperature, in addition to absorption by resonance lines. Results are consonant with those from other laboratory and atmospheric transmittance measurements, and they underline the importance of properly modeling the water-vapor continuum in calculations of atmospheric radiation in the middle infrared.