Harunobu Masuko

Stratospheric ozone isotope enrichment studied by submillimeter wave heterodyne radiometry: the observation capabilities of SMILES

The isotopic ratio of molecules often provides valuable information about past or presently occurring processes in the atmosphere because chemical and physical processes may give rise to isotope fractionation of molecular species. However, there are so far no published satellite measurements on the spatial and temporal variations of ozone isotopes in the stratosphere. Spectroscopic remote sensing methods can theoretically be used to observe ozone isotope fractionation on a global scale, but sufficient accuracy has not yet been achieved. A new generation of submillimeter-wave receivers employing sensitive superconductor-insulator-superconductor (SIS) detector technology will provide new opportunities for precise remote sensing measurements of ozone isotopes on a global scale. We have estimated the observation capabilities of two different SIS instruments, namely the space-station-borne Japanese Experimental Module/Sub-Millimeter-wave Limb Emission Sounder (JEM/SMILES) instrument, currently planned for launch in 2008, as well as the airborne Submillimeter wave Atmospheric Sounder/Airborne Submillimeter SIS Radiometer (SUMAS/ASUR) sensor. Measurements of the airborne sensor, conducted in 1996, are presented in order to demonstrate the detection of normal-O/sub 3/ and asymmetric-18-O/sub 3/ in the SMILES frequency bands. In the ideal case, JEM/SMILES has the capability to measure the ozone isotope enrichment (/spl delta//sup M/O/sub 3/) in the middle stratosphere with a precision of /spl sim/12/sup 0///sub 00/, /spl sim/11/sup 0///sub 00/, and /spl sim/9/sup 0///sub 00/, for asymmetric-18-O/sub 3/, symmetric-17-O/sub 3/, asymmetric-17-O/sub 3/, respectively, for a daily zonal mean product with resolution of 10/spl deg/ in latitude. The systematic error, including contributions of all instrumental and spectroscopic uncertainties, is estimated to be of the order of 100/sup 0///sub 00/ to 200/sup 0///sub 00/ and should be reduced by prelaunch laboratory measurements and in-flight calibrations. A remaining bias in the SMILES measurements will have to be quantified by dedicated validation campaigns. JEM/SMILES should then be capable to provide valuable information on the global distribution and seasonal variation of ozone isotope fractionation in the stratosphere. This new technology will allow us to shed new light on this still open issue in atmospheric sciences.

CRL/NASDA airborne dual-frequency polarimetric interferometric SAR system

An airborne X and L-band Synthetic Aperture Radar system was developed by the joint project of Communication Research Laboratory and National Space Development Agency of Japan from 1993 to 1996. It is installed on the airplane, Gulfstream II. The resolution is 1.5 m/3.0 m (for X/L-band) in both azimuth and range direction. The both SAR are operated with polarimeter capability. The X-band SAR has cross-track interferometry function. In this report we describe our SAR system, ground processing system and the performance of our system. Furthermore we will discuss motion compensation and interferogram quality.

Airborne microwave rain-scatterometer /radiometer

Abstract An airborne microwave rain-scatterometer/radiometer system operated at 10 and 34-45 GHz was developed for the remote sensing of precipitation, especially rain, from an aeroplane. Airborne rain-scatterometers were developed as a first step for the development of the future spaceborne rain-scatterometer. Flight experiments of more than 30 hours were performed in co-operation with the ground-based C-band weather radar. The sensor system of the airborne microwave rain-scatterometer/radiometer, flight experiment in June 1981 cooperating with the ground-based weather radar, and results of data analyses are described.

BSMILES - a balloon-borne superconducting submillimeter-wave limb-emission sounder for stratospheric measurements

A balloon-borne superconducting submillimeter-wave limb-emission sounder (BSMILES) was developed to observe thermal emission lines from stratospheric minor constituents. BSMILES carries a 300-mm-diameter offset parabolic antenna, a 624-639-GHz superconductor-insulator-superconductor (SIS) receiver, a three-axis fiber-optical gyroscope, and an acousto-optical spectrometer. BSMILES was launched from the Pacific Coast of Japan. All systems operated properly and emission line spectra of stratospheric gases, such as O/sub 3/, HCl, HO/sub 2/, and O/sub 3/ isotopes were measured. The system noise temperature in double sideband (DSB) during the flight was less than 460 K over the observing bandwidth with a best value of 330 K that is 11 times as large as the quantum limit (11h/spl nu//k/sub B/). After the observation, the gondola splashed down in the Pacific Ocean and was retrieved. Almost all instruments were waterproofed, and it has been proved that they are reusable.

Submillimeter Limb-emission Sounder JEM/SMILES aboard the Space Station

A submillimeter limb-emission sounder, that is to be aboard the Japanese Experiment Module (JEM, dubbed as KIBO) at the International Space Station, has been designed. This payload, Superconducting Submillimeter-wave Limb-emission Sounder (SMILES), is aimed at global mappings of stratospheric trace gases by means of the most sensitive submillimeter receiver ever operated in space. Such sensitivity is ascribed to a Superconductor-Insulator- Superconductor (SIS) mixer, which is operated at 4.5 K in a dedicated cryostat combined with a mechanical cooler. SMILES will observe ozone-depletion-related molecules such as ClO, Hcl, HO2, HNO3, BrO and O3 in the frequency bands at 624.32-626.32 GHz and 649.12-650.32 GHz. A scanning antenna will cover tangent altitudes from 10 to 60 km in every 53 seconds, while tracing the latitudes form 38 S to 65 N along its orbit. This global coverage makes SMILES a useful tool of observing the low- and mid- latitudinal areas as well as the Arctic peripheral region. The molecular emissions will be detected by two units of acousto-optic spectrometers (AOS), each of which has coverage of 1.2 GHz with a resolution of 1.8 MHz. This high-resolution spectroscopy will allow us to detect weak emission lines attributing to less-abundant species.

SIR-B Experiments in Japan: Sensor Calibration and Oil Pollution Detection Over Ocean

Preliminary results of the SIR-B experiments conducted in Japan are reported mainly on the sensor calibration and the oil pollution experiments. No significant result was obtained for the rice crop experiment which was carried out at the same time, mainly due to the late flight of SIR-B. The sensor calibration experiment was eventually reduced to only the evaluation of the imaging characteristics of SIR-B. However, a reasonable relation between the image count and RCS is found, and the resolution analysis by using the corner reflector images gives satisfactory results. A possible cause leading to what are rather overestimates of the resolution is pointed out to be the background clutter. A simulated oil slick area over sea was clearly detected on the SIR-B image, although the incident angle was not so appropriate for the purpose. This result demonstrates the capability of a space-borne synthetic aperture radar for effective surveillance of oil spills over high seas.

Evaluation of Vector Winds Observed by NSCAT in the Seas around Japan

In order to validate wind vectors derived from the NASA Scatterometer (NSCAT), two NSCAT wind products of different spatial resolutions are compared with observations by buoys and research vessels in the seas around Japan. In general, the NSCAT winds agree well with the wind data from the buoys and vessels. It is shown that the root-mean-square (rms) difference between NSCAT-derived wind speeds and the buoy observations is 1.7 ms−1, which satisfies the mission requirement of accuracy, 2 ms−1. However, the rms difference of wind directions is slightly larger than the mission requirement, 20°. This result does not agree with those of previous studies on validation of the NSCAT-derived wind vectors using buoy observations, and is considered to be due to differences in the buoy observation systems. It is also shown that there are no significant systematic trends of the NSCAT wind speed and direction depending on the wind speed and incidence angle. Comparison with ship winds shows that the NSCAT wind speeds are lower than those observed by the research vessels by about 0.7 ms−1 and this bias is twice as large for data observed by moving ships than by stationary ships. This result suggests that the ship winds may be influenced by errors caused by ships motion, such as pitching and rolling.

A 650-GHz Band SIS Receiver for Balloon-Borne Limb-Emission Sounder

A superconducting low-noise receiver has been developed for atmospheric observations in the 650-GHz band. A waveguide-type tunerless mixer mount was designed based on one for the 200-GHz band. Two niobium SIS (superconductor-insulator-superconductor) junctions were connected by a tuning inductance to cancel the junction capacitance. We designed the ωRnCj product to be 8 and the current density to be 5.5 kA/cm2. The measured receiver noise temperature in DSB was 126-259 K in the frequency range of 618-660 GHz at an IF of 5.2 GHz, and that in the IF band (5-7 GHz) was 126-167 K at 621 GHz. Direct detection measurements using a Fourier transform spectrometer (FTS) showed the frequency response of the SIS mixer to be in the range of about 500-700 GHz. The fractional bandwidth was about 14%. The SIS receiver will be installed in a balloon-borne limb-emission sounder that will be launched from Sanriku Balloon Center in Japan.

Submillimeter-wave spectroscopic performance of JEM/SMILES

An acousto-optical spectrometer (AOS) is employed in order to meet scientific mission objectives of submillimeter-wave limb-emission sounder (SMILES) to be aboard the Japanese Experiment Module (JEM) of the International space station (ISS). The capability of multi channel detection with AOS is suitable for observing multi chemical species in a wide frequency region. Wide noise dynamic range enables us to obtain the spectra without unnecessary increase of system noise, suggesting a good combination of AOS with low noise front end system of SMILES> Several technical concerns relating to important instrumental characteristics of AOS are discussed and expected performance of the spectrometers to be used in the JEM/SMILES mission are over viewed.

Quantitative Measurements of Path-Integrated Rain Rate by an Airborne Microwave Radiometer over the Ocean

Abstract Data on the airborne microwave radiometer, which is one of the sensors of the airborne microwave rain-scatterometer/radiometer (AMRS) system, are analyzed to infer path-integrated rain rate measured from topside. The equation of radiative transfer is used to relate quantitatively the antenna temperature to the rain rate profile inferred by the scatterometer. The influence of the ocean surface temperature on the radiometer measurements of rain is evaluated by a model computation. The theoretical prediction agrees excellently with the measurements. The effect of nonuniform rain along the propagation path is also evaluated by using the experimental data. It is shown that the excess antenna temperature (difference between the antenna temperature under raining and no-rain conditions) in the 10 GHz band is proportional to the path-integrated rain rate, and a method for determining the reference temperature (antenna temperature under a no-rain condition) is suggested.