Hirohiko Ishikawa

Kyoto University, Kioto, Kyōto, Japan

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Publications (33)30.87 Total impact

  • Weiqiang Ma, Yaoming Ma, Hirohiko Ishikawa
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    ABSTRACT: Evapotranspiration (ET) is a boundary condition for regional scale hydrological and climatological modeling. Spatial knowledge of land surface ET is of principal interest for environmental evaluation especially in semi-arid regions. The study used the Surface Energy Balance System (SEBS) model based on Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) remote sensing and field observations data that have been used and tested for deriving ET over the NamCo area in the Tibetan Plateau, located in the southwest of China. Two ASTER scenes were used for estimating the ET over the study area. To validate the proposed methodology, the ground-measured ET was compared to the ASTER derived ET values for the study area. The results show that the derived ET in different months over the study area is in good accordance with the in-situ data. The derived ET value over the study area is much closer to the field measurement; the RMSE is 0.7 mm/d. It is therefore concluded that the SEBS methodology is successful for the retrieval of ET using the ASTER and in-situ data over the study area.
    Atmospheric Research 01/2014; 138:91–97. · 2.20 Impact Factor
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    ABSTRACT: The idea of ground-based evapotranspiration (ET) is of the most interesting for land–atmosphere interactions, such as water-saving irrigation, the performance of irrigation systems, crop water deficit, drought mitigation strategies and accurate initialization of climate prediction models especially in arid and semiarid catchments where water shortage is a critical problem. The recent year's drought in Australia and concerns about climate change has prominent the need to manage water resources more sustainably especially in the Murrumbidgee catchment which utilizes bulk water for food security and production.This paper discusses the application of a Surface Energy Balance System (SEBS) model based on Landsat-5 TM data and field observations has been used and tested for deriving ET over Coleambally Irrigation Area (CIA), located in the southwest of NSW, Australia. 16 Landsat-5 TM scenes were selected covering the time period of 2009, 2010 and 2011 for estimating the actual ET in CIA. To do the validation the used methodology, the ground-measured ET was compared to the Landsat-5 TM retrieved actual ET results for CIA. The derived ET value over CIA is much closer to the field measurement. From the remote sensing results and observations, the root mean square error (RMSE) is 0.74 and the mean APD is 7.5%. The derived satellite remote sensing values belong to reasonable range.
    Atmospheric Environment 11/2012; 59:408–414. · 3.11 Impact Factor
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    Yuichiro Oku, Hirohiko Ishikawa
    Advances in Geosciences, Volume 16: Atmospheric Science (AS). 05/2010;
  • Hydrological Research Letters. 01/2010; 4:1-5.
  • Yuichiro Oku, Mizuo Kajino, Hirohiko Ishikawa
    International Journal of Remote Sensing 01/2010; 31:5439-5447. · 1.14 Impact Factor
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    ABSTRACT: Parameterization of turbulent flux from bare-soil and undercanopy surfaces is imperative for modeling land–atmosphere interactions in arid and semiarid regions, where flux from the ground is dominant or comparable to canopy-sourced flux. This paper presents the major characteristics of turbulent flux transfers over seven bare-soil surfaces. These sites are located in arid, semiarid, and semihumid regions in Asia and represent a variety of conditions for aerodynamic roughness length (z 0m ; from 1 to 10 mm) and sensible heat flux (from 50 to 400 W m 2). For each site, parameter kB 1 [ln(z 0m /z 0h), where z 0h is the thermal roughness length] exhibits clear diurnal variations with higher values during the day and lower values at night. Mean values of z 0h for the individual sites do not change significantly with z 0m , resulting in kB 1 increasing with z 0m , and thus the momentum transfer coefficient increases faster than the heat transfer coefficient with z 0m . The term kB 1 often becomes negative at night for relatively smooth surfaces (z 0m 1 mm), indicating that the widely accepted excess resistance for heat transfer can be negative, which cannot be explained by current theories for aerodynamically rough surfaces. Last, several kB 1 schemes are evaluated using the same datasets. The results indicate that a scheme that can reproduce the diurnal variation of kB 1 generally performs better than schemes that cannot.
    Journal of Applied Meteorology and Climatology 03/2008; 47:276-290. · 2.02 Impact Factor
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    ABSTRACT: In this study, a parameterization method based on Landsat-7 Enhanced Thematic Mapper (ETM) data and field observations is presented and tested for deriving the regional land surface variables, vegetation variables and land surface heat fluxes over a heterogeneous landscape. As a case study, the method and two Landsat-7 ETM images are applied to the Jiddah area of Saudi Arabia. The regional distribution maps of surface reflectance, normalized difference vegetation index, modified soil adjusted vegetation index (MSAVI), vegetation coverage, leaf area index, surface temperature, net radiation flux, soil heat flux, sensible heat flux and latent heat flux have been determined over the Jiddah area. The derived results have been validated by using the ‘ground truth’. The results show that the more reasonable regional distributions of land surface variables (surface reflectance, surface temperature), vegetation variables (MSAVI and vegetation coverage), net radiation, soil heat flux and sensible heat flux can be obtained by using the method proposed in this study. Further improvement of the method is also discussed. Copyright © 2006 John Wiley & Sons, Ltd.
    Hydrological Processes 06/2007; 21(14):1892 - 1900. · 2.50 Impact Factor
  • Yuichiro Oku, Hirohiko Ishikawa, Zhongbo Su
    Journal of Applied Meteorology and Climatology 01/2007; 46(2):183-. · 2.02 Impact Factor
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    ABSTRACT: Low-frequency microwave brightness temperature is strongly affected by near-surface soil moisture; therefore, it can be assimilated into a land surface model to improve modeling of soil moisture and the surface energy budget. This study presents a new variational land system used to assimilate AMSR-E brightness temperature of vertical polarization of 6.9 GHz and 18.7 GHz. The system consists of a land surface model (LSM) used to calculate surface fluxes and soil moisture, a radiative transfer model (RTM) to estimate the microwave brightness temperature, and an optimization scheme to search for optimal values of soil moisture by minimizing the difference between modeled and observed brightness temperature. The LSM is an improved simple biosphere model for sparse vegetation modeling and the RTM is a Q-h model that can account for the effects of surface roughness and vegetation. Several parameters in the LSM and RTM can significantly affect the outputs of the land data assimilation system but their values are either highly variable or unavailable. To solve this problem, we developed a dual-pass assimilation technique. Pass 1 inversely estimates the optimal values of the model parameters with long-term (∼months) forcing data and brightness temperature data, while Pass 2 estimates the near-surface soil moisture in a daily assimilation cycle. This system is driven by well-established reanalysis data and global data sets of leaf area index, precipitation, and surface radiation, and was tested at a CEOP (Coordinate Enhanced Observing Period) reference site on the Tibetan Plateau. The system not only detected the effect of precipitation events that were missing in the forcing data, but also led to a significant improvement in modeling of the surface energy budget.
    Journal of the Meteorological Society of Japan 01/2007; 85A:229-242. · 0.80 Impact Factor
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    01/2007;
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    ABSTRACT: Similarity between temperature and water vapour was investigated in the Fourier domain by using their coherency spectra, defined as the correlation coefficient between their Fourier modes, and the relative efficiency of their vertical transport. The class-averaged values of these indices were computed from the turbulence measurements over sparse grasslands on the Tibetan plateau during the intensive observations of GEWEX (Global Energy and Water Experiment) Asian Monsoon Experiment (GAME). It was found that the energy-containing eddies at scales up to 100z (z being height) are characterised by well-maintained similarity between these scalars. The scalars are highly correlated with each other, and their transport efficiencies are almost equal within this scale range. In contrast, similarity was not always maintained at scales larger than 1000z. Detailed analyses showed that this breakdown of similarity occurs occasionally or sporadically, suggesting that it is caused by events whose average return period is not much smaller than the current averaging time, i.e. 30min. We speculate that entrainment of drier and warmer air at the top of the atmospheric boundary layer caused the scalar dissimilarity at this scale range.
    Boundary-Layer Meteorology 12/2006; 122(1):85-103. · 2.29 Impact Factor
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    ABSTRACT: Sensible and latent heat fluxes from the plateau surface are of great importance in the Asian monsoon system. Since the plateau occupies a wide area and the environmental conditions are severe to perform surface observation, the satellite remote sensing is inevitably a practical tool to estimate these fluxes from whole plateau surface. The in situ flux estimation is, however, necessary as a ground truth for the satellite remote sensing. It also gives scientific information in constructing land surface-atmosphere model, which shares an important part of data assimilation system using satellite data. There are several different approaches in estimating in situ heat fluxes. The simplest method uses operational observation and experimental parameters, and it gives steady continuous estimation. The more sophisticated Bowen ratio or profile observation gives the more precise information. The estimation with turbulence measurement together with the measurement of radiation and soil heat fluxes give detailed description of land surface-atmosphere interaction suitable to model development. Since 1998, a combination of these methods has been applied to the Tibetan plateau. The efforts of these in situ flux observation and the current understandings are summarized in this presentation.
    Advances in Earth Science. 12/2006; 21(12):1237-1243.
  • Advances in Earth Sciences. 12/2006; 21:2006.
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    ABSTRACT: Based on CAMP/Tibet [Coordinated Enhanced Observing Period (CEOP) Asia-Australia Monsoon Project (CAMP) on the Tibetan Plateau] turbulent data collected at the Bujiao (BJ) site of the Nagqu area, the turbulent structure and transportation characteristics in the near surface layer during summer are analyzed. The main results show that the relationship between the normalized standard deviation of 3D wind speed and stability satisfies the similarity law under both unstable and stable stratifications. The relations of normalized standard deviation of temperature and specific humidity to stability only obey the “−1/3 power law” under unstable conditions. In the case of stable stratifications, their relations to stability are dispersing. The sensible heat dominates in the dry period, while in the wet period, the latent heat is larger than the sensible heat.
    Advances in Atmospheric Sciences 01/2006; 23(4):579-585. · 1.34 Impact Factor
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    ABSTRACT: The diurnal, seasonal, and interannual variations in land surface temperature (LST) on the Tibetan Plateau from 1996 to 2002 are analyzed using the hourly LST dataset obtained by Japanese Geostationary Meteorological Satellite 5 (GMS-5) observations. Comparing LST retrieved from GMS-5 with independent precipitation amount data demonstrates the consistent and complementary relationship between them. The results indicate an increase in the LST over this period. The daily minimum has risen faster than the daily maximum, resulting in a narrowing of the diurnal range of LST. This is in agreement with the observed trends in both global and plateau near-surface air temperature. Since the near-surface air temperature is mainly controlled by LST, this result ensures a warming trend in near-surface air temperature.
    Journal of Climate - J CLIMATE. 01/2006; 19(12):2995-3003.
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    ABSTRACT: In this study, a parameterization method based on Landsat-7 ETM data and field observations has been proposed and tested for deriving surface reflectance, surface temperature, NDVI, MSAVI, vegetation coverage, LAI, net radiation flux, soil heat flux, sensible heat flux and latent heat flux over heterogeneous landscape. As a case study, the methodology was applied to the experimental area of the CAMP/Tibet, which located at the central Tibetan Plateau. Two scenes of Landsat-7 ETM data were used in this study. The scene of 9 June 2002 was selected as a case of summer, and the scene of 2 December 2002 was selected as a case of winter. To validate the proposed methodology, the ground-measured surface reflectance, surface temperature, net radiation flux, soil heat flux, sensible heat flux and latent heat flux are compared to Landsat-7 ETM derived values. The results show that the derived surface variables and land surface heat fluxes in two different months over the study area are in good accordance with the land surface status. These parameters show a wide range due to the strong contrast of surface features. Also, the estimated land surface variables and land surface heat fluxes are in good agreement with ground measurements, and all their absolute percent difference is less than 9.9% in the validation sites. It is therefore concluded that the proposed methodology is successful for the retrieval of land surface variables and land surface heat fluxes using the Landsat-7 ETM data and filed observations over the study area.
    Journal of Geophysical Research 01/2006; 111. · 3.17 Impact Factor
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    ABSTRACT: Distributions of regional land surface variables, vegetation variables and land surface heat fluxes over the AECMP’95 area were analyzed using a new parameterized method of combining satellite remote sensing with field observations. The results show that reasonable regional distribution of surface reflectance, surface temperature, modified soil adjusted vegetation index, vegetation coverage, net radiation, soil heat flux and sensible heat flux over heterogeneous arid area in northwestern China can be obtained by using this method. This technique is still in the development stage, the derived latent heat flux shows a bit higher trend than the observed values over the whole study area. The recommendations of improving the scheme are also presented.
    Journal of Arid Environments - J ARID ENVIRON. 01/2004; 57(2):257-273.
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    ABSTRACT: Land-atmosphere interactions on the Tibetan Plateau are important because of their influence on energy and water cycles on both regional and global scales. Flux variance and eddy covariance methods were used to measure turbulent fluxes of heat, water vapor, and momentum over a Tibetan shortgrass prairie during the Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiment (GAME) in 1998. Under unstable conditions during the monsoon period (July–September), the observed standard deviations of temperature and specific humidity (normalized by appropriate scaling parameters) followed the Monin-Obukhov theory. The similarity constants for heat C T and water vapor C q in their dimensionless functions of stability under a free convection limit were both 1.1, unlike the differences (i.e., C T C q) reported in other studies. While the transfer efficiency of heat and water vapor exchange generally agreed with the prediction from the Monin-Obukhov theory, momentum exchange was less efficient than predicted. In comparison with the eddy covariance data, the flux variance method (with C T = C q = 1.1) underestimated both heat and water vapor fluxes by <5%. When the eddy covariance data were absent, the flux variance method was used for gap filling the seasonal flux database. To estimate latent heat flux during the premonsoon period in June, C T /C q was approximated as r Tq (where r Tq is a correlation coefficient for the fluctuations of temperature and water vapor) because of the sensitivity of C q to changes in soil moisture conditions. The dramatic changes in the Bowen ratio from 9.0 to 0.4 indicate the shift of energy sources for atmospheric heating over the plateau, which, in turn, resulted in the shift of turbulent exchange mechanisms for heat and water vapor. Citation: Choi, T., et al. (2004), Turbulent exchange of heat, water vapor, and momentum over a Tibetan prairie by eddy covariance and flux variance measurements, J. Geophys. Res., 109, D21106, doi:10.1029/2004JD004767.
    Journal of Geophysical Research 01/2004; 109(D211106). · 3.17 Impact Factor
  • Journal of Japan Society of Hydrology & Water Resources. 01/2004; 17(4):392-400.
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    ABSTRACT: Turbulent flux measurements based on the eddy correlation technique were conducted on the Tibetan Plateau during the Intensive Observation Period (IOP) of the GEWEX Asian Monsoon Experiment (GAME) in 1998. This paper presents on analysis of the surface energy budget and its closure at the Amdo planetary boundary layer site in the eastern Tibetan Plateau using GAME-Tibet IOP data. A seasonal variation in the surface energy closure ratio (CR) was seen. CR was higher than 0.8 in the pre-monsoon period and after DOY 233, when the infrared hygrometer was performing satisfactorily. However, CR was lower than 0.7 throughout most of the summer monsoon, due at least in part to degraded performance of the infrared hygrometer under heavy precipitation. In addition, through detail analysis of the diurnal variations of surface energy flux for the best-CR period of September 4–6, it was found that the melting and freezing of near-surface soil moisture plays a significant role in the variation of surface energy fluxes, particularly in terms of latent heat flux. The calculated effective mass of melting and freezing water in one day was 3.3–3.9 kg/m2, which is comparable to the daily total.
    Journal of Hydrology 12/2003; 283(1):169-183. · 2.96 Impact Factor