All issues
Volume 60
Displaying 1-3 of 3 articles from this issue
- |<
- <
- 1
- >
- >|
-
Yuzo Mano2009 Volume 60 Pages 1-6
Published: 2009
Released on J-STAGE: June 18, 2009
JOURNAL FREE ACCESSRecent infrared sounders such as AIRS and IASI have thousands of channels. Because computational efficiency is crucial for practical soundings, it is important to reduce the number of channels that are used. One approach is channel selection, in which a limited number of channels with large information content are selected from among all the channels of a sounder. Here we study another approach. Virtual channels, which are referred as Maximum Information Composite Channels (MICC) hereafter, are constructed by a linear combination of original channels so as to maximize the entropy reduction in atmospheric retrieval. We found that the number of MICCs that had almost the same entropy reduction as the original channels was about a tenth the number of original channels when the MICC method was applied to 185 channels of AIRS. MICCs can be used in the same way as conventional channels in atmospheric retrieval. The channel number reduction leads to a reduction of the matrix size and the computational cost in the retrieval. A numerical experiment on temperature and humidity retrievals showed that the CPU time for the MICC approach was significantly smaller than that of the conventional approach with almost the same retrieval error.View full abstractDownload PDF (1099K) -
Yuzo Mano, Toru Hashimoto, Arata Okuyama2009 Volume 60 Pages 7-16
Published: 2009
Released on J-STAGE: June 18, 2009
JOURNAL FREE ACCESSThe Meteorological Satellite Center (MSC) of the Japan Meteorological Agency began retrieving aerosol optical thickness over land in March 2007 using the AVHRR/NOAA visible channel. Exact nonspherical scattering with realistic particle shape distribution is fully considered. We compared the MSC optical thickness with AERONET version 1.5 optical thickness at nine AERONET stations in northeastern Asia. Although we found statistically significant correlations at all stations, the dispersions were large, especially at southern stations. We thus examined the samples with large errors at each station to investigate the causes of the errors. The following suggestions were obtained:
(1) The MSC optical thickness shows overestimation for severe Yellow Sand events and underestimation for very thick gray haze. This suggests that the absorption property of aerosol particles used in our theoretical calculation is unrealistic. A revision of the complex refractive index of aerosol used in making the look-up table may be required.
(2) The influence of small cumuli or cloud edges is seen in the medium range of optical thickness (< ∼2). When cloud-contaminated samples are removed by reference to MODIS high-resolution images, the correlations between the MSC and AERONET optical thickness are notably improved and are as high as 0.6 at the most of the stations. However, systematic underestimations were found at many stations.
(3) These underestimations are likely to be caused by the aerosol-free assumption used in the land surface reflectance modelling because the samples on adjacent ocean grids showed excellent correlations and no systematic bias. This is confirmed by the fact that the monthly minimums of optical thickness at AERONET stations show notable positive values.View full abstractDownload PDF (1497K) -
Takeyasu Yamamoto, Akio Kobayashi2009 Volume 60 Pages 17-24
Published: 2009
Released on J-STAGE: November 09, 2009
JOURNAL FREE ACCESSCrustal strain has been observed using borehole-type multi-component strainmeters at Tsuruga and Imazu stations in the northern part of the Kinki district, Japan. We investigated 12.5 years of strain data recorded at these stations starting from 1996. Seasonal strain changes observed at Imazu correlate well with the changes in ground water level observed there. Seasonal strain changes observed at Tsuruga are well described by the output of a tank model with daily precipitation as input. Strain changes corresponding to the initial stabilization of the strainmeters are modeled by exponential functions. After seasonal and exponential strain changes are removed, the strain history shows excursions around 2000 and 2005. These cannot be explained by temporal changes in strainmeter sensitivity or long-term variations of precipitation. We calculated expected strain changes at the two stations caused by the slow slip events in the Tokai district from 2000 to 2005 and found that calculated principal axes of strain are consistent with observations, although the amounts of observed strain are about ten times larger than calculated ones.View full abstractDownload PDF (1146K)
- |<
- <
- 1
- >
- >|