久世 宏明

Many types of data compression for SAR raw data have been developed during the past 30 years. Since most of them focus on reducing the number of bits required to store signal information onboard, the resulting complexity has been a great hindrance to the implementation of an efficient compression algorithm. We propose a new method of data compression that can be carried out onboard a small-sized platform. The method imposes no additional requirement on the antenna size by reducing the number of pulses needed to produce an image and compensating the missing pulses based on information provided from other pulses. The most complicated task of reconstructing the missing pulses can be performed in the ground station, not onboard the small platform. Because fewer pulses are needed, less power will be required for transmitting and receiving the pulses. This is advantageous for reducing the pulse repetition frequency (PRF), which normally becomes higher for smaller antennas. This method will be applied to our circularly polarized synthetic aperture radar (CP-SAR) system, which is currently being developed toward a mission onboard a microsatellite.

In our previous work, we developed a method in which ground-based, spectral measurements of direct and scattered solar radiation are employed to retrieve optical properties of tropospheric aerosols, using the three component aerosol model (TCAM), as well as column amount of molecular constituents of the atmosphere such as water vapor. We observed solar spectra under clear-sky conditions between Aug, 2007 and May, 2009 at Chiba, Japan and derived the seasonal trend of aerosol characteristics around the site. In this work, we apply these aerosol optical parameters to the atmospheric correction of Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data to obtain seasonal maps of ground surface reflectance and aerosol optical depth around Chiba. The surface reflectance (at 550 nm wavelength) derived from the TCAM model is 0.05 - 0.09, exhibiting seasonal variation depending on the vegetation coverage. As compared with the results based on standard aerosol models such as the maritime or continental model, the difference among models is generally small (< 0.002) in winter and large (> 0.005) in summer. In addition, we show preliminary results of retrieving column amount of molecules (H2O, O-3, CO2, and CH4) from skylight spectra observed by the schemes of multi-axis differential optical absorption spectroscopy (MAX-DOAS).

Concentrations of atmospheric CO2 and aerosol were measured in a field campaign conducted in winter 2006 around Mt. Tsukuba, Japan using ground-based CO2 analyzers, a lidar, and sky radiometers as well as CO2 analyzers onboard an aircraft. Vertical measurements revealed occasional similarity between the profiles of CO2 and aerosol concentrations, though their temporal variations are not always coordinated because of the effects of local sources or sinks. A sudden increase of downward winds, due to the approach of an anticyclonic synoptic flow, resulted in a rapid decrease in both the CO2 and aerosol concentrations in the boundary layer. These observation results have demonstrated that simultaneous measurements with airborne and ground-based instruments set on the summit/foot of a mountain are useful for the study of variability of CO2 concentration in the boundary layer. Citation: Saito, R., T. Tanaka, H. Hara, H. Oguma, T. Takamura, H. Kuze, and T. Yokota (2009), Aircraft and ground-based observations of boundary layer CO2 concentration in anticyclonic synoptic condition, Geophys. Res. Lett., 36, L07807, doi: 10.1029/2008GL037037.

Continuous lidar observation of the atmosphere is important for monitoring various phenomena such as air pollution, local meteorology, and plume diffusion. Center for Environmental Remote Sensing (CEReS), Chiba University, developed a portable automatic lidar (PAL) with the cooperation of Hamamatsu Photonics Inc. After installing the automatic alignment capability, the PAL system has provided continuous observation data in every 20 s except for some maintenance periods. The lidar operates at 532 nm (second harmonic of Nd:YAG laser), with 1.4 kHz pulse-repetition frequency, 50 ns pulse width, and 15 μJ pulse energy. The signal is received by a 20-cm diameter telescope pointed northward with an elevation angle of 38°, and processed by a photon counter. The range resolution is 24m (height resolution is 15m). During the operation period of 3 years, we have observed atmospheric oscillations of Brunt-Vaisala type with oscillation periods of several to several 10 minutes, raindrops yielding information on falling speeds and corresponding droplet sizes, upward/downward motion of air in the boundary layer, and statistics on the cloud bottom height. In this chapter, we describe various features of PAL data that characterize meteorological phenomena, including precipitation, frontal passage, and development of boundary layer.

A portable automated lidar (PAL) system, which conducts full-time operation and all-weather observation through the laboratory window, has been developed. Observations of long-term temporal and spatial dynamics of the atmosphere are described and the advantage of full-time operation is discussed

An equilateral triangular microstrip antenna is proposed for circularly-polarized synthetic aperture radar (CP-SAR) systems operated in L-Band (1.27 GHz). For airborne application, a prototype antenna patch is designed, fabricated and tested. Electromagnetically-coupled, dual-feeding method is applied to generate the circularly-polarized wave radiating from the patch. The fabricated patch exhibits an axial ratio bandwidth (&lt 3 dB) of about 0.58% (7.4 MHz), which is consistent with the value of 0.57% (7.24 MHz) from the simulation.

We describe a fiber laser system operated at 1.6 mu m developed for a compact satellite mission, in which the vertical column density of atmospheric CO2 is measured with detector systems deployed along the satellite track.

Laser-induced photodissociation of ozone molecules is studied by irradiating isotope-mixed ozone gas with a narrow-band laser beam of around 1 μm wavelength. Significant decomposition is detected only for the irradiated ozone isotopologue with the decomposition amount nearly proportional to the laser power. This result indicates that the process is not due to multi-photon absorption, but rather due to single-photon absorption through the rotationally resolved transitions in the 3A2 ← 1A1 (v2 = 1-0) band. © 2008.

The influence of humidity is considered on the concentration of the suspended particulate matter (SPM) measured with a beta-ray counter. The humidity condition inside a small observatory where the counter is located is, in general, different from the ambient condition outside the observatory. From the measured values, the ambient SPM concentration is derived considering the hygroscopic effect of common aerosol species of sea salt (SS), (NH4)(2)SO4, NH4NO3 and NaNO3. In a case study conducted during September 2005, temperature and humidity were measured both inside and outside the observatory. The average value of the relative humidity is 48% for inside and 78% for outside, resulting in approximately 53% larger SPM mass concentration after the correction. Accordingly, the value of mass extinction efficiency, which is given by the ratio between the optically measured extinction coefficient and the mass concentration, becomes lower after the correction. (c) 2006 Elsevier Ltd. All rights reserved.

We have developed and operated a portable automated lidar (PAL) system that is capable of unattended, continuous operation under all-weather conditions. Here we report the features of the observed signals that convey the information on the temporal and spatial dynamics of the aerosols and clouds in the troposphere, illustrating the advantage of the continuous operation through nighttime and daytime.

All-sky Survey High Resolution Air-shower (Ashra) telescope has been developed to detect cosmic-ray particles. An imaging lidar system has been constructed by applying the Ashra telescope technique to atmospheric monitoring. The two-dimensional information on the aerosol distribution near the ground level can be obtained from the bistatic, imaging-lidar measurement.

Lidar data observed by two continuously operated portable automated lidar (PAL) systems and images from the visible and thermal infrared channels of the advanced very high resolution radiometer (AVHRR) sensor on board the NOAA 16 satellite are employed for the characterization of cloud heights and cloud types. The PAL systems are located in Chiba and Ichihara city areas, separated by approximately 10km. Measurements from October 2003 to March 2005 reveal that monthly averages of cloud base height and cloud cover ratio show good agreement between the two sites. The characteristics of the vertical (Chiba) and slant (Ichihara) measurements are also discussed. The PAL data are used to adjust threshold values of a cloud-type classification method in split-window data of NOAA 16-AVHRR. Comparisons between the lidar signals and the cloud classification results from the concurrent AVHRR images show that the classification method can reasonably be applied to this mid-latitude case, although the split-window technique was originally developed for tropical clouds. (c) 2007 The Optical Society of Japan.

Continuous data of aerosol optical thickness monitored using differential optical absorption spectroscopy (DOAS) are correlated with the concentration of ground-measured suspended particulate matter (SPM). A high correlation is found between the DOAS and the ground SPM data, making it possible to calculate the mass extinction efficiency of the aerosols in the atmosphere. It is found that the value of mean mass extinction efficiency (MEE) varies over a range of 2.6-13.7 m2 g-1, with smaller and larger values occurring for size distributions dominated by coarse and fine particles, respectively.

Continuous data of aerosol optical thickness monitored using differential optical absorption spectroscopy (DOAS) are correlated with the concentration of ground-measured suspended particulate matter (SPM). A high correlation is found between the DOAS and the ground SPM data, making it possible to calculate the mass extinction efficiency of the aerosols in the atmosphere. It is found that the value of mean mass extinction efficiency (MEE) varies over a range of 2.6-13.7 m(2) g(-1), with smaller and larger values occurring for size distributions dominated by coarse and fine particles, respectively.

With the method of differential optical absorption spectroscopy (DOAS), average concentrations of aerosol particles along light path were measured with a flashlight source in Chiba area during the period of one month. The optical thickness at 550 nm is compared with the concentration of ground-measured suspended particulate matter (SPM). Good correlations are found between the DOAS and SPM data, leading to the determination of the aerosol mass extinction efficiency (MEE) to be possible in the lower troposphere. The average MEE value is about 7.6m(2)center dot g(-1), and the parameter exhibits a good correlation with the particle size as determined from the wavelength dependence of the DOAS signal intensity.

For the purpose of calibrating multiwavelength lidar data, we developed a scatterometer to measure the aerosol scattering coefficient at the ground level. The system is based on an integrating sphere, cw lasers (532 and 633 nm), and a controlled flow of the ambient air, including aerosol particles. The simulation study and experimental results indicate that the detection efficiency of this instrument is approximately 10%-40% better than that of an integrating nephelometer, because of the wider acceptance angle of the scattered light. The scattering coefficients measured at the two wavelengths, as well as the resulting value of the angstrom exponent, show good correlation with the results simultaneously measured with an integrating nephelometer and an optical particle counter. (c) 2005 Optical Society of America

The All-sky Survey High Resolution Air shower detector (Ashra) is primarily designed to elucidate transient objects such as Gamma Ray Bursts not only detecting optical lights but also simultaneously TeV gamma, PeV neutrinos, and EeV cosmic rays. Ashra records images in unprecedented arc-minute detail of high-energy cosmic particle intefactions in the atmosphere using new wide angle high resolution optics, Image Intensifier and CMOS technology. A first run of data taking with prototype versions of the optical and the trigger systems took place in 2004-2005, allowing us to evaluate the performance of the systems and to approach an analysis strategy. Full configuration of the Mauna Loa site will be reached by 2006. We will illustrate the summary of the Ashra project and the pilot data with the analysis for optical transient and TeV gamma-ray search.

A bistatic imaging lidar system is being developed on the basis of a novel telescope concept. The schematic of bistatic lidar measurement and the retrieval algorithm of the bistatic imaging lidar data are described, with the results of simulation studies.

Continuous data of the atmosphere monitored using a portable automated lidar (PAL) are correlated with the ground-measured SPM concentration. When the boundary layer is well mixed, a high correlation is found between the lidar and the ground data, making it possible to calculate a conversion factor between them.

For the purpose of calibrating multi-wavelength lidar data, a scatterometer has been developed to measure the aerosol scattering coefficient at the ground level. The system is based on an integrating sphere, cw lasers (532 nm and 633 rim), and controlled flow of the ambient air. Simulation study indicates that the detection efficiency of this instrument is better than that of an integrating nephelometer. The scattering coefficients measured at the two wavelengths, as well as the resulting value of the Angstrom parameter, show good correlation with the results simultaneously measured with an integrating nephelometer and an optical particle counter.

During the ACE-Asia intensive observation period (IOP), an intercomparison experiment with ground-based lidars and aircraft observations was conducted near Tokyo. On 23 April 2001, four Mie backscatter lidars were simultaneously operated in the Tokyo region, while the National Center for Atmospheric Research C-130 aircraft flew a stepped-ascent profile between the surface and 6 km over Sagami Bay southwest of Tokyo. The C-130 observation package included a tracking Sun photometer and in situ packages measuring aerosol optical properties, aerosol size distribution, aerosol ionic composition, and SO2 concentration. The three polarization lidars suggested that the observed modest concentrations of Asian dust in the free troposphere extended up to an altitude of 8 km. We found a good agreement in the backscattering coefficient at 532 nm among lidars and in situ 180degrees backscatter nephelometer observations. The intercomparison indicated that the aerosol layer between 1.6 and 3.5 km was a remarkably stable and homogenous in mesoscale. We also found reasonable agreement between the aerosol extinction coefficients (sigma(a) similar to 0.03 km(-1)) derived from the airborne tracking Sun photometer, in situ optical instruments, and those estimated from the lidars above the planetary boundary layer (PBL). We also found considerable vertical variation of the aerosol depolarization ratio (delta(a)) and a negative correlation between delta(a) and the backscattering coefficient (delta(a)) below 3.5 km. Airborne measurements of size-dependent optical parameters (e.g., the fine mode fraction of scattering) and of aerosol ionic compositions suggests that the mixing ratio of the accumulation-mode and coarse-mode ( dust) aerosols was primarily responsible for the observed variation of delta(a). Aerosol observations during the intercomparison period captured the following three types of layers in the atmosphere: a PBL ( surface to 1.2-1.5 km) where fine (mainly sulfate) particles with a low delta(a) (< 10%) dominated; an intermediate layer (between the top of the PBL and 3.5 km) where fine particles and dust particles were moderately externally mixed, giving moderate delta(a); and an upper layer (above similar to 3.5 km) where dust dominated, giving a high delta(a) (30%). A substantial dust layer between 4.5 and 6.5 km was observed just west of Japan by the airborne instruments and found to have a lidar ratio of 50.4 +/- 9.4 sr. This agrees well with nighttime Raman lidar measurements made later on this same dust layer as it passed over Tokyo, which found a lidar ratio of 46.5 +/- 10.5 sr.

Alignment of the laser beam and telescope axes is crucial to the acquisition of high quality lidar data. For a continuously operated Mie lidar, a routine alignment correction is needed to ensure that its data are not influenced by the misalignment and thus truly represent the aerosol and cloud behavior. This paper describes the operation of such a lidar system with automatic correction of optical alignment.

We propose and demonstrate a novel method of differential optical absorption spectroscopy (DOAS), in which an obstruction flashlight equipped on a tall stack is exploited for monitoring concentration of atmospheric NO2. This pulsed DOAS measurement also brings about information on the aerosol optical thickness through the horizontal atmospheres.

Classification results using texture analysis is presented for forest fire smoke from satellite remote sensing data. Texture analysis is carried out for normalized difference images calculated from visible and thermal infrared images of the Indonesian forest fire in 1997. Smoke regions are identified by assuming threshold values for the resulting texture feature as well as for radiances in the original and difference images. It is found that when the thresholds are chosen appropriately for GMS visible and infrared spin scan radiometer, 94% pixels exhibit agreement between the classification results using the texture analysis and the supervised Euclidean classification. Agreement is found for 96% pixels in mutual verification using the VISSR image and a concurrent NOAA advanced very high resolution radiometer image. A correlation coefficient of 0.91 is obtained between the results from the two sensors in the variation of the number of smoke pixels accumulated for 12 days in September 1997. Additionally, it is confirmed that as the threshold value of the texture feature is increased, the variation range of the aerosol optical thickness is also increased. As a whole, this study indicates that texture analysis provides quite reasonable results in the smoke detection when appropriately combined with the spectral information. (C) 2002 Elsevier Science Ltd. All rights reserved.

In this paper, we describe the application of the texture analysis to the extraction of the aerosol distribution around the Chiba area from NOAA AVHRR data. First, the information on the aerosol distribution is obtained from a satellite image ("the test image"). For this purpose, we use the sea surface (Tokyo bay and the Pacific Ocean) that surrounds the Chiba prefecture. The 6S code is operated under plausible atmospheric conditions, and the value of aerosol optical thickness, tau(A), is determined by the condition that the calculated total radiance agrees with the observed total radiance. This method is applied to several sites arbitrary chosen on the sea area, and by interpolation, we obtain a "tau(A) image". Second, we generate a "difference image" by subtracting a "clear image" from the "test image". The clear image is prepared by applying the atmospheric correction that is based on the radiation transfer calculation using the MODTRAN code to an AVHRR image. The difference image is considered to include the information of the aerosol distribution. By applying the texture analysis to this image, we extract the regions in which the atmospheric features are considered to be uniform (we call them texels). Using this additional information, it is possible to improve the "tau(A) image" so that if both land and sea surfaces are included in a texel, the aerosol optical thickness above the land area is assumed to be the same as that above the sea area. As a whole, the present method makes it possible to extend the method of analyzing atmospheric conditions from satellite data to the land surfaces that are surrounded by water areas. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.

This paper describes the lidar inversion of the tropospheric aerosol extinction profiles under the influence of multiple-scattering effects for various elevation angles of lidar detection. A single-scattering lidar equation is employed to analyze lidar signals with multiple-scattering contributions that are calculated by the Monte Carlo method for given atmospheric conditions. We calculate errors in the optical thickness from the results with and without multiple-scattering effects. It is found that the errors vary, in a range of 2-18% according to the optical thickness variation of 0.19-3.8. The dependence of the error on the field-of-view angle of the lidar observation is also discussed.

A multi-wavelength Mie lidar is a powerful tool to investigate the optical properties of aerosol particles along with their vertical profile information. In the usual analysis with the Fernald method, however, it is required to assume both the lidar ratio S1 and the extinction coefficients at the far end boundary. For a multi-wavelength lidar, appropriate choices of these parameters are indispensable to derive consistent profiles from the actual data. In this work, we propose two algorithms for the analysis of four-wavelength lidar data. The first algorithm is more comprehensive in that it adopts the direct fitting of the lidar A-scopes to the theoretical curves that are based on a look-up table: the table is pre-calculated for various combinations of the extinction coefficient, S1 parameter, complex refractive index, and aerosol size distribution. As a result, the vertical profiles of these parameters are determined along with the extinction profile. The second approach is a pragmatic one, and it relies on the sun photometer data simultaneously measured with the lidar data. By assuming a constant S1 value for each wavelength in the lower troposphere, a consistent set of S1 is determined by fitting the observed profiles to reference profiles that are relevant to the aerosol optical thicknesses from the sun photometer measurement.

Ground-based, optical monitoring of the NO2 column density and aerosol optical thickness is described. The instrument consists of a solar radiation spectrometer (SRS) and a conventional sunphotometer, both mounted on the same sun-tracker and operated automatically. From daytime measurements in Chiba, Japan during 1998-2000, variations of NO2 and aerosol are analyzed. A correlation coefficient between NO2 and aerosol is larger than 0.90 in winters. Because of the capability of simultaneous, real time measurement, this method is particularly suitable for air pollution studies in city areas.

We report on wavelength modulation detection of trace amount of acetylene at 1.5 mum. A Fabry-Perot cavity (FPC) is employed to enhance the effective absorption length. The wavelength modulation is applied by synchronously modulating the laser cavity and the FPC cell.

This paper describes an iterative method for extracting single-scattering contributions in the retrieval of aerosol extinction profiles from lidar signals. The iterative procedure is formulated by use of the lidar solution with introducing a multiple-scattering ratio as a correction factor, which is calculated by the Monte Carlo method. The iterative method is applied to an experimental signal observed by a multi-wavelength lidar.

The amount of trace moisture is precisely determined in N-2 and HCl gases by means of near-infrared diode-laser absorption spectroscopy. As an optical source, we use a near-infrared InGaAsP distributed-feedback diode laser which operates at room temperature. A multi-pass sample cell designed for corrosive gases is employed to enhance molecular absorption. For the purpose of reducing the etalon noise that is usually encountered in multi-pass absorption spectroscopy, we adjust the base path length in accordance with the bandwidth of a molecular spectral line so that the etalon frequency does not critically overlap with that of the molecular spectrum.. The remaining noise is further reduced by applying multi-stage smoothing. Trace moisture content as small as 2.3 ppb is detected with a 20-m absorption length.