MAXI, the first astronomical payload attached to ISS JEM‐EF, began operation on August 3, 2009 for monitoring all‐sky X‐ray images every ISS orbit (92 min). This paper reports the first results obtained during the 1‐month test observations. All instruments as well as two main X‐ray slit cameras, the GSC and SSC, worked as we expected. The detection limits of MAXI‐GSC are about 25 mCrab and 8 mCrab for one ISS orbit (92 min) and 1‐day observations, respectively. GSC covers about 76% and 96% of the entire sky for respective single‐orbit and 1‐day observations. MAXI has detected a transient X‐ray pulsar A0535+26, an X‐ray burst, and a gamma‐ray burst in the first month of the test observation period.
Current measurements from DIARAD/VIRGO, PMO6V/VIRGO and ACRIM3 radiometers are of the same order of magnitude, but differ from TIM/SORCE by about 4.5 W m−2. This difference is higher than the sum of the claimed individual absolute uncertainties of the instruments. In this context, the SOLAR payload on the International Space Station embarks the SOVIM package. We give the results of the differential absolute radiometer DIARAD/SOVIM and discuss its associated uncertainties. Compared to DIARAD/VIRGO, all possible efforts have been made to improve the absolute accuracy. Substantial progress has been made in the aperture area and electrical power measurements. The measured TSI value from the left channel of DIARAD/SOVIM during three days of June 2008 is 1364.50 ± 1.38 W m−2 (Total) or ±0.49 W m−2 (if we combine the individual contributions in quadrature). The right channel gives 1364.75 W m−2 with the same uncertainties. These values are about 1.2 W m−2 lower than DIARAD/VIRGO and about 4 W m−2 higher than TIM/SORCE. The difference between the left and right channels measurements is as low as 0.25 W m−2 which is within the improved uncertainty limits.
Upper tropospheric water vapor and clouds play an important role in Earth's climate, but knowledge of them, in particular diurnal variation in deep convective clouds, is limited. An essential variable to understand them is cloud ice water content. The Japanese Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on board the International Space Station (ISS) samples the atmosphere at different local times allowing the study of diurnal variability of atmospheric parameters. We describe a new ice cloud data set consisting of partial Ice Water Path and Ice Water Content. Preliminary comparisons with EOS-MLS, CloudSat-CPR and CALIOP-CALIPSO are presented. Then, the diurnal variation over land and over open ocean for partial ice water path is reported. Over land, a pronounced diurnal variation peaking strongly in the afternoon/early evening was found. Over the open ocean, little temporal dependence was encountered. This data set is publicly available for download in HDF5 format.
Performance evaluation of normalized difference chlorophyll index in northern Gulf of Mexico estuaries using the Hyperspectral Imager for the Coastal Ocean
The Hyperspectral Imager for the Coastal Ocean (HICO) was used to derive chlorophyll-a (chl-a) based on the normalized difference chlorophyll index (NDCI) in two Gulf of Mexico coastal estuaries. Chl-a data were acquired from discrete in situ water sample analysis and above-water hyperspectral surface acquisition system (HyperSAS) remote sensing reflectance in Pensacola Bay (PB) and Choctawhatchee Bay (CB). NDCI algorithm calibrations and validations were completed on HICO data. Linear and best-fit (polynomial) calibrations performed strongly with R2 of 0.90 and 0.96, respectively. The best validation of NDCI resulted with an R2 of 0.74 and root-mean-square error (RMSE) of 1.64 µg/L. A strong spatial correspondence was observed between NDCI and chl-a, with higher NDCI associated with higher chl-a and these areas were primarily located in the northern PB and eastern CB at the river mouths. NDCI could be effectively used as a qualitative chl-a monitoring tool with a reduced need for site-specific calibration.
Comparison is presented for neutron components of radiation environment in the near-Earth and near-Mars space, which is based on data from high energy neutron detector (HEND) instrument onboard NASA Mars Odyssey and data from BTN-M1 instrument onboard Russian segment of International Space Station.
Flight Experiment Results of the Polysiloxane-Block-Polyimide “BSF-30” on the JEM/MPAC&SEED Mission on the ISS
Atomic oxygen (AO) in low Earth orbit (LEO) is one of the most dangerous environmental factors leading to erosion of the external materials of a spacecraft. As one of the methods to improve AO tolerance, the use of silicon-containing materials has been proposed. On such materials, an SiO2 layer is formed from the reaction of the silicon contained in the material and the AO existing in orbit, which can therefore be called a “self-organized” layer. In the present study, polysiloxane-block-polyimide “BSF-30”, which is a silicon-containing polyimide, was investigated by ground testing and in a flight experiment. BSF-30 was exposed to the LEO space environment on the Japanese Experimental Module/Micro Particles Capturer & Space Environment Exposure Device (JEM/MPAC&SEED) mission on the ISS for 8.5 months. As a result, a mass loss of 0.011 mg was measured, which is about 1/500 times smaller than that of a common polyimide. From a cross sectional transmission electron microscopy analysis the formation of a layer about ~50 nm thick was observed on the exposed surface, within which high fractions of Si and O were also detected. In conclusion, it is verified that BSF-30 has sufficient AO tolerance in a LEO environment by the JEM/MPAC&SEED.
In-Orbit Measurement of the AOS (Acousto-Optical Spectrometer) Response Using Frequency Comb Signals
The in-orbit response characteristic of the AOS (Acousto-Optical Spectrometer) was estimated from spectral profiles taken by using a frequency comb generator, which was originally used for frequency axis calibration. Frequency comb signals taken under various environmental conditions in orbit were consolidated to deduce the response profile of the spectrometer. The fluctuation bandwidth calculated from the deduced spectral response compared well with that derived from the noise characteristic of the spectrometer.
A New Fluvial Analog for the Ridge-Forming Unit, Northern Sinus Meridiani/Southwest Arabia Terra Mars
Geomorphic analysis suggests that the Ridged Unit of northern Meridiani/southwest Arabia Terra may be an ancient, martian megafan that was emplaced by fluvial flow off the Southern Highlands.
We report on the MAXI GSC X-ray monitoring of the Crab nebula and pulsar during the GeV gamma-ray flare on 2010 September detected by AGILE and Fermi-LAT. There were no significant variations on the pulse-phase-averaged and pulsed fluxes during the gamma-ray flare. The pulse profile also showed no significant change during the period. The upper limits on the variation of the pulse-phase-averaged and pulsed fluxes on MJD 55457.5–55462.5 in the 4–10 keV band are 1% and 19% at the 90% confidence limit of the statistical uncertainty, respectively. Here, the measured fluxes include a 2% systematic uncertainty at the 1-σ limit due to the error on the instrument calibration. The lack of variations in the pulsed component in multi-wavelength range (radio, soft X-ray, hard X-ray, and gamma-ray) supports the nebula origin for the gamma-ray flare.
We report on the MAXI GSC X-ray monitoring of the Crab nebula and pulsar during the GeV gamma-ray flare for the period of 2010 September 18–24 (MJD 55457 − 55463), detected by AGILE and Fermi-LAT. There were no significant variations on the pulse phase averaged and pulsed fluxes during the gamma-ray flare on time scales from 0.5 to 5 days. The pulse profile also showed no significant change during this period. The upper limits on the variations of the pulse phase averaged and pulsed fluxes for the period MJD 55457.5 − 55462.5 in the 4–10 keV band were derived to be 1% and 19%, respectively, at the 90% confidence limit of the statistical uncertainty. The lack of variations in the pulsed component over the multi-wavelength range (radio, X-ray, hard X-ray, and gamma-ray) supports not a pulsar, but a nebular origin for the gamma-ray flare.