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.

The statistics of ground-based retrievals of cloud liquid water path using the microwave water radiometer (MWR) are typically assumed to be independent of the cloud's absolute position in the column. Furthermore, translational invariance implies statistical parity, i.e. invariance under reflection, of cloud-base height (z_bot) and cloud-top height distributions. This symmetry is necessarily broken, especially under conditions of high boundary-layer relative humidity for which a minimum large-scale lifting condensation level leads to the generation of a significant positive skewness in the distribution function of z_bot. We suggest that the signature of this boundary effect is visible in ARM MWR time-series collected at the TWP site. Motivated by the MWR analysis, we incorporate a minimum lifting condensation level into the analytic model of unresolved low-cloud optical variability developed by Jeffery & Austin (J. Atmos. Sci., to appear). Preliminary results indicate that the effect of cloud-base height skewness on mean oceanic low-cloud reflectivity averaged over GCM spatial scales (order 100 km) is significant.

A thermal infrared imaging system has been developed for studying the spatial and temporal statistics of clouds. The Infrared Cloud Imager (ICI) system acquires radiometrically calibrated images of downwelling atmospheric radiation that are used to identify and classify clouds according to their radiometric brightness. The ICI system has been deployed in the Arctic during the winter of 2000-2001at Poker Flat Research Range near Fairbanks, Alaska, and during February - May, 2002 at Barrow, Alaska. This paper describes the ICI system and its calibration, shows images of various clouds, and discusses ongoing research to develop automated algorithms for cloud classification.

Inexpensive optical MEMS gas and chemical sensors offer chip-level solutions to environmental monitoring, industrial health and safety, indoor air quality, and automobile exhaust emissions monitoring. Previously, Ion Optics, Inc. reported on a new design concept exploiting Si-based suspended micro-bridge structures. The devices are fabricated using conventional CMOS compatible processes. The use of photonic bandgap (PBG) crystals enables narrow band IR emission for high chemical selectivity and sensitivity. Spectral tuning was accomplished by controlling symmetry and lattice spacing of the PBG structures. IR spectroscopic studies were used to characterize transmission, absorption and emission spectra in the 2 to 20 micrometers wavelength range. Prototype designs explored suspension architectures and filament geometries. Device characterization studies measured drive and emission power, temperature uniformity, and black body detectivity. Gas detection was achieved using non-dispersive infrared (NDIR) spectroscopic techniques, whereby target gas species were determined from comparison to referenced spectra. A sensor system employing the emitter/detector sensor-chip with gas cell and reflective optics is demonstrated and CO₂ gas sensitivity limits are reported.

Astronomical arrays operating at (sub)millimeter wavelengths are seriously compromised by rapid variations in atmospheric water vapor that distort the phase coherence of incoming celestial signals. The signal received by each antenna of the array suffers a phase delay that varies rapidly with time and from antenna to antenna. Unless corrected, these distortions limit the coherence time of the array and seriously compromise its sensitivity and image quality. Building on the success of a prototype infrared radiometer for millimeter astronomy (IRMA), which operates in the 20μm region to measure the column abundance of atmospheric water vapor, this paper presents results obtained with a second generation IRMA operating at the James Clerk Maxwell telescope (JCMT) between January and July 2001. The results are compared with other measures of water vapor available on the summit of Mauna Kea, including: the JCMT SCUBA bolometer camera, the California Institute of Technology (CSO) opacity monitors, the JCMT 183GHz water vapor radiometer and Hilo-launched radiosonde data.

A combined active-passive remote sensing system has been developed to study atmospheric radiation and cirrus cloud radiative properties at the NOAA Mauna Loa Observatory on the island of Hawaii. The active portion of this system is an eye-safe, dual-polarization lidar, while the passive portion is a Fourier transform spectro-radiometer operating in emission mode. The combined system allows unattended, remote measurements of infrared atmospheric emission and clouds with depolarization discrimination of ice and liquid.

No abstract available.

The Rotating Shadowband Spectroradiometer (RSS) is a tandem-prisms spectrograph that uses a CCD array to measure solar direct and diffuse irradiances. Two versions of the RSS were designed at the Atmospheric Sciences Research Center at the State University of New York at Albany to measure UV from 295-370 nm and VIS-NIR from 360-1050 nm. A number of prototypes have been deployed at two sites of DOE's Atmospheric Radiation Measurement program since 1996. The first commercial UV RSS built by Yankee Environmental Systems, Inc. was deployed in 2001 and the VIS-NIR RSS is slated for permanent installation at the ARM SGP site in 2002. The paper describes instrument characterization procedures, spectral and radiometric calibrations. Mathematical algorithms applied to the spectra to correct wavelength shifts, to reduce stray light effects, and to correct drifts in radiometric calibration are described.

Assuming a curved exponential atmosphere with beam attenuation and isotropic scattering both proportional to density, we model three regimes that each become dominant in turn as the sun sets. This drastic simplification of the earth's real atmosphere both provides insight to guide system design and is able to fit over an irradiance range exceeding nine decades a set of narrowband measurements of blue light intensity made in the natural environment on clear days. The single-scattering regime involves only overall illumination (or cloudiness) as an adjustable parameter and appears especially relevant to animal geolocation based on measurement of diffuse irradiance.

Sequential measurements of direct and diffuse solar radiation for each scattering angle in the visible and near infrared region,were carried out with the ground based sun-sky radiometer Prede, in order to determine directly in situ the instrumental errors. The sensitivity of the code Skyrad 3, produced by T. Nakajima, to the experimental errors has been studied in this work. The uncertainty on the retrieved columnar aerosol volume distribution, aerosol optical thickness, single scattering albedo, and phase function, was obtained for each wavelength. Measurements were taken in two locations with very different atmospheric characteristics: Antarctica and Rome, Italy. The method used for the determination of experimental error showed to give good results, independently of the location. The uncertainties obtained for the quantities retrieved by Skyrad 3, are independent of the atmospheric turbidity and, possibly, they can be assumed as general accuracy levels.

When a multi-channel radiometer is calibrated using the sun as calibration source, the error in the calculated calibration constants may be large when solar zenith angles increase. A multi-regression model has proved to be suitable to derive narrowband irradiance from broadband irradiance, ozone column and solar zenith angles (SZA). In this paper, a modification of this model is being proposed to improved the multi-channel instrument sun calibration against spectroradiometers, considering a channel of a multi-channel radiometers as a broadband instrument. The errors in the GUV irradiance, compared to the spectroradiometer irradiance, diminished considerably at all channels for SZA larger than 50^a, then, this technique could be particularly beneficial to calibrate radiometers installed at high latitudes, where SZA during winter, even at noon, are larger than 50^a.

The newly available Advanced Very High Resolution (AVHRR) Polar Pathfinder (APP) data set of 18 years from 1982 to 1999, subsampled to a 25 km scale, was used to retrieve cloud amount, cloud optical depth, cloud particle size, cloud temperature, cloud particle phase, surface temperature, surface broadband albedo, radiation fluxes and shortwave and longwave cloud forcing over the Arctic ocean and surrounding land areas. The spatial and temporay distributions of those retrieved Arctic climate parameters together with an analysis of the seasonal and interannual variability in those parameters, especially surface temperature, surface broadband albedo, cloud amount and precipitable water, are presented. Results show that the Arctic climate has indeed warmed up as indicated by surface temperature, cloud amount, cloud particle size and phase at confidence level of higher than 95% for Spring and Summer times, but cooled down in winter. The surface broadband albedo has decreased significantly in Autumn indicating the late onset of sea ice and snow, especially for the Arctic ocean area. The Arctic ocean surface temperature has decreased during the wintertime at confidence level of 97%, especially for the central and eastern Arctic oceans. The Arctic Oscillation(AO) has strong correlation relationship with the surface temperature and cloud amount for some Arctic areas at the confidence level of almost 100%. For different areas in the entire Arctic region, the correlation relationship is different. The surface temperature and cloud amount in Greenland have negative correlation with the AO simultaneously, while that correlation turns to be positive in the north Europe area, indicating the different Arctic areas have different effects and feedback on the global climate system or vice versa.

Since the satellites provide frequent and global observations of atmospheric and terrestrial environment, attempts have been made to use satellite data for long-term monitoring of land reflectances, vegetation indices and clouds properties. Although the construction and characteristics of spaceborne instruments may be quite similar, they are not identical among all missions, even for the same type of instrument like AVHRR. Consequently, the effect of varying spectral response may create an artificial noise imposed upon a subtle natural variability. We report the results of a study on the sensitivity of Normalized Difference Vegetation Index (NDVI), surface and cloud reflectance to differences in instrument spectral response functions (SRF) for various satellite sensors. They include AVHRR radiometers onboard NOAA satellites NOAA-6 - NOAA-16, the Moderate Resolution Imaging Spectroradiometer (MODIS), the VEGETATION sensor (VGT) and the Global Imager (GLI). We also analyzed the SRF effects for several geostationary satellites used for cloud studies, such as GOES-8 - 12, METEOSAT-2 - 7, GMS -1 - 5. The results obtained here demonstrate that the effect of instrument spectral response function cannot be ignored in long-term monitoring studies that employ space observations from different sensors. The SRF effect introduces differences in observed reflectances and retrieved quantities that may be comparable or exceed the range of natural variability and possible systematic trends, the contribution from the calibration, atmospheric and other corrections. Some modeling results were validated against real satellite observations with good agreement.

Long-path ozone integrated measurements with a CO₂-laser DIAL system were performed in Madrid City during the 'vehicle-free' day. The results showed a strong correlation between human activity and ozone photochemical generation. The ozone concentration follows, even quantitatively, the same trend of the overall traffic intensity as long as both the UVB radiation and NO₂ are present. An average decrease of 12.3 ±1.2 % of the intensity of vehicle traffic during the 'free-vehicle' day resulted in a lowering the ozone burden by almost 14.4 ± 1.4 % . This new type of information can stimulate the development of local models to understand the dynamic underlying urban pollution. The results indeed show the effectiveness of such a measure as to reduce the ozone burden on human and plants health.

At most optical wavelengths, laser light in a cloud lidar experiment is not absorbed but merely scattered out of the beam, eventually escaping the cloud via multiple scattering. There is much information available in this light scattered far from the input beam, information ignored by traditional 'on-beam' lidar. Monitoring these off-beam returns in a fully space- and time-resolved manner is the essence of our unique instrument, Wide Angle Imaging Lidar (WAIL). In effect, WAIL produces wide-field (60-degree full-angle) 'movies' of the scattering process and records the cloud's radiative Green functions. A direct data product of WAIL is the distribution of photon path lengths resulting from multiple scattering in the cloud. Following insights from diffusion theory, we can use the measured Green functions to infer the physical thickness and optical depth of the cloud layer, and, from there, estimate the volume-averaged liquid water content. WAIL is notable in that it is applicable to optically thick clouds, a regime in which traditional lidar is reduced to ceilometry. Here we present recent WAIL data on various clouds and discuss the extension of WAIL to full diurnal monitoring by means of an ultra-narrow magneto-optic atomic line filter for daytime measurements.

The optical turbulence in atmosphere, especially in the atmospheric boundary layer, plays an important role in the propagation of laser beam. It can make the fluctuation of density and distortion of wave front. The balloon borne radiosonde with temperature fluctuation sensors is often used to study the turbulence profiles in the atmospheric boundary layer. But it can not get the continuous temporal and spatial variance of turbulence structure. In this paper, Doppler sodar and microwave wind profiler are used to study the optical turbulence structure in the atmospheric boundary layer. The fluctuation in the index of refraction can be defined as optical turbulence, so the structure constants of refractive index C_n² is often used in such problems. Not only the wind profiler but also the high solution temporal and spatial turbulence structure can be gained with Doppler radar. From these experimental results, we study the relative structure of turbulence on different height, study the spectra of C_n² on different. These results are compared to previous results get with temperature fluctuation sensors. In addition, the seasonal variance of turbulence structure is also discussed in the paper.