Improved Limb Atmospheric Spectrometer Research Articles

Stratospheric aerosol surface area and volume inferred from HALOE, CLAES, and ILAS measurements

Relationships are presented for converting remote measurements of stratospheric aerosols to surface area and volume densities. Measurements from the Halogen Occultation Experiment (HALOE), the cryogenic limb array etalon spectrometer (CLAES), and the improved limb atmospheric spectrometer (ILAS) were considered. The relationships were derived using an extensive record of in situ aerosol size distribution measurements made in sulfate aerosols and in polar stratospheric clouds (PSCs). Conversions were derived for sulfate aerosols using the appropriate refractive indices, and for PSCs using the refractive indices for either nitric acid trihydrate or liquid ternary H2SO4‐H2O‐HNO3 aerosols. Coincident measurements from HALOE, CLAES, and in situ particle counters are in generally good agreement at middle latitudes, for surface area and volume. Analysis of CLAES measurements under cold polar conditions suggests that these data should be used with caution.

Improved technique for data inversion and its application to the retrieval algorithm for ADEOS/ILAS

An improved numerical inversion scheme is discussed. The way the scheme is formulated allows one to include the iterative stabilization of inversion by solving constrained least square system using linear iterations. Therefore, the technique discussed is closely related to both matrix inversion and iterative inversion methods, which are often considered as alternative to each other. As a result, this inversion procedure provides both a statistically optimum and highly stable solution even in the case of a very large number of unknowns. Also, various a priori information can be used: non-negativity of solution (by logarithmic transformation), smoothness of retrieved characteristics, a priori estimations of solution, etc. The proposed technique is applied to provide statistical optimization of the retrieval algorithm for the Improved Limb Atmospheric Spectrometer (ILAS) aboard the Advanced Earth Observing Satellite (ADEOS). ILAS has 1024 visible channels and 44 IR channels to measure atmospheric transmittance at different atmospheric levels. More than 400 parameters (temperature, pressure, gas and aerosol profiles) should be determined from ILAS data. To realize statistical optimization for such a situation is quite a challenging problem. The main advantages and difficulties of applying this inversion technique for this optimization are discussed.

ADEOS/ILAS aerosol retrieval algorithm with 5 channels

The information content of aerosol properties is discussed for a set of extinction coefficient measurements of the ILAS (Improved Limb Atmospheric Spectrometer) instrument. ILAS was launched on the ADEOS (Advanced Earth Observing Satellite) spacecraft in 1996 and has a wide spectral coverage in the infrared region (between 6.21 and 11.77 μm). From these extinction measurements, ILAS has a capability to provide the vertical profiles of gaseous species, which are important for studies of the ozone hole phenomena, as well as the stratospheric aerosol compositions. In this paper, we describe an algorithm to infer the chemical composition of aerosols, i.e., types of PSCs (polar stratospheric clouds), the size distributions, total volume and total surface areas of aerosols by using five window channels, i.e. one at visible wavelength (0.78μm) and four (7.12, 8.27, 10.60, 11.76μm) at infrared wavelengths. Our algorithm mainly consists of two parts. The first part is to determine the chemical composition of PSCs and sulfate aerosols. The second one is to derive the mean size, volume and surface area. The main purposes of this paper are to provide the extinction spectrum over the whole infrared channels in order to estimate the reliable amounts of trace gases and also to estimate the information of aerosol surface distribution for heterogeneous chemical reaction studies on PSCs.

ILAS (Improved Limb Atmospheric Spectrometer) /ADEOS data retrieval algorithms

Data retrieval algorithms (version 1) have been developed for the Improved Limb Atmospheric Spectrometer (ILAS) project. The ILAS sensor is designed to measure atmospheric constituents and parameters with a solar occultation technique. Vertical profiles of temperature, pressure, and aerosol extinction coefficient are determined from visible channels covering the 753 ∼ 784 nm wavelength range for O 2 molecular absorption. Profiles of O 3, CH 4, N 2O, HNO 3, H 2O, NO 2, CFC-11, and aerosols are simultaneously obtained from IR channels (6.2 ∼ 11.8 μm wavelength range) with temperature and pressure profiles as already estimated. The retrieval is realized by vertical inversion with non-linear spectral fitting for each height. A numerical simulation test revealed that each target parameter (pressure, temperature, aerosol, and gas concentrations) can be retrieved by these algorithms to well within required precisions.

Improved Limb Atmospheric Spectrometer (ILAS) measurements of the stratospheric ozone layer: Its early results

Improved Limb Atmospheric Spectrometer (ILAS) measurements of the stratospheric ozone layer: Its early results

Early results from improved limb atmospheric spectrometer (ILAS) measurements

Improved Limb Atmospheric Spectrometer (ILAS), which was developed by Environment Agency of Japan, was a satellite‐borne sensor to observe chemical and dynamical environment of the stratospheric ozone layer from space. ILAS had been normally operating on board the Advanced Earth Observing Satellite (ADEOS) from the beginning of November 1996 to the end of June 1997 when the sudden failure of ADEOS solar battery system happened. Using the solar occultation technique, the ILAS measured vertical profiles of ozone (03) and ozone‐related species such as nitric acid (HNO3), nitrogen dioxide (NO2), nitrous oxide (N2O), methane (CH4), and water vapor (H2O). It also measured vertical profiles of atmospheric temperature and pressure as well as aerosol extinction coefficient at 780 nm. Extinction coefficients in the infrared wavelength region were also derived and used to infer aerosol types and extinction spectra over the whole infrared channels. ILAS‐derived data will be used for better understanding of the stratospheric ozone layer changes.

Status of ADEOS mission sensors

The main objectives of the Advanced Earth Observation Satellite (ADEOS) are to contribute to global observation of environmental change with the international community as well as to establish future platform technologies. To achieve these objective, ADEOS will carry two core sensors developed by NASDA, the Ocean Color and Temperature Scanner (OCTS) and the Advanced Visible and Near-Infrared Radiometer (AVNIR), and six Announcement of Opportunity (AO) sensors, the Interferometric Monitor for Greenhouse Gases (IMG) provided by the Ministry of International Trade and Industry of Japan, the Improved Limb Atmospheric Spectrometer (ILAS) and the Retroreflector In Space (RIS) provided by the Environment Agency of Japan, the NASA Scatterometer (NSCAT) and the Total Ozone Mapping Spectrometer (TOMS) provided by NASA, and the Polarization and Directionality of the Earth's Reflectances (POLDER) provided by CNES. ADEOS, for which basic design began last summer, is scheduled to be launched into sun synchronous orbit from Tanegashima Space Center by H-II rocket in early 1995. The interface coordination between ADEOS and mission sensors was the most important topic of this international cooperative project. This paper reports the status of the ADEOS mission sensors from the viewpoint of the interface coordination, and addresses the outline and development status of NASDA core sensors.