Soushi Kato

Surface heat balance analysis of Tainan City on March 6, 2001 using ASTER and Formosat-2 data

The urban heat island phenomenon occurs as a mixed result of anthropogenic heat discharge, decreased vegetation, and increased artificial impervious surfaces. To clarify the contribution of each factor to the urban heat island, it is necessary to evaluate the surface heat balance. Satellite remote sensing data of Tainan City, Taiwan, obtained from Terra ASTER and Formosat-2 were used to estimate surface heat balance in this study. ASTER data is suitable for analyzing heat balance because of the wide spectral range. We used Formosat-2 multispectral data to classify the land surface, which was used to interpolate some surface parameters for estimating heat fluxes. Because of the high spatial resolution of the Formosat-2 image, more roads, open spaces and small vegetation areas could be distinguished from buildings in urban areas; however, misclassifications of land cover in such areas using ASTER data would overestimate the sensible heat flux. On the other hand, the small vegetated areas detected from the Formosat-2 image slightly increased the estimation of latent heat flux. As a result, the storage heat flux derived from Formosat-2 is higher than that derived from ASTER data in most areas. From these results, we can conclude that the higher resolution land coverage map increases accuracy of the heat balance analysis. Storage heat flux occupies about 60 to 80% of the net radiation in most of the artificial surface areas in spite of their usages. Because of the homogeneity of the building roof materials, there is no contrast between the storage heat flux in business and residential areas. In sparsely vegetated urban areas, more heat is stored and latent heat is smaller than that in the forested suburbs. This result implies that density of vegetation has a significant influence in decreasing temperatures.

First space-borne high-spatial-resolution optical imagery of the Antarctic from Formosat-2

Coordinating and collecting satellite data of changing polar environments is one of the prime activities of International Polar Year (IPY) 2007–08 (Rapley et al. 2004). Within this framework, the requirements to obtain spaceborne snapshots of the Polar Regions and key high latitude processes have been prepared by the international cryospheric community under the auspices of the approved IPY project titled the Global Inter-agency IPY Polar Snapshot Year (GIIPSY). Earlier efforts in manoeuvring Radarsat-1 in a special mode provided radar images with a spatial resolution of 30 m over the entirety of Antarctica during September–October 1997 (Jezek et al. 1998). Limited to their altitude (AL), swath (SW) and pointing capability (PC), however, the operation of optical satellites with high-spatial-resolution sensors is generally restricted to certain latitudes. For example, Landsat (AL:705 km/SW:185 km/PC:0°) mission has been able to provide high-spatial-resolution optical imagery only to ~81°N to ~81°S since the 1980s. The coverage is now extended to ~86° by ASTER (AL:705 km/SW:60 km/PC:24°) (Kargel et al. 2005), but there has been no availability of space-borne optical image of the polar regions with a resolution equivalent or higher than Landsat type sensors with latitudes higher than 86°, until the successful operation of Formosat-2 (AL:891 km/SW:24 km/PC: ± 45° across and along track). Equipped with two-axes high torque reaction wheels, Formosat-2 is able to point not only to ± 45° across track, but also to ± 45° along track (Liu et al. 2007). Figure 1 shows the accessible areas (longer lines: along track ± 0°, across track ± 45°; shorter lines: along track ± 0°, across track ± 30°) and the corresponding ground tracks (solid curves) of Formosat-2 in the Polar Regions. Note that the accessible areas would be even greater if the pointing direction is also set to ± 45° along track. The detailed comparison of Formosat-2 with other similar sensors, including the multi-spectral bands and imaging repeat period, can be found in table I in Liu et al. (2007). To support IPY 2007–08, the National Space Organization (NSPO) of Taiwan launched a Polar Imaging Campaign (PIC) in March 2006. Up to September 2007, a total of 1 131 624 km2 in the North Polar Region and a total of 57 408 km2 in the South Polar Region had been imaged by Formosat-2. All Formosat-2 images taken during the NSPO PIC are available from the authors.

ASTER/TIR vicarious calibration activities in US and Japan validation sites for 14 years

The ASTER instrument onboard the NASA’s Terra satellite launched in December 1999 has three subsystems divided by the spectral regions. ASTER thermal infrared (TIR) subsystem has five TIR bands with a spatial resolution of 90 m. Since March 2000 after the initial checkout period, many vicarious calibration (VC) experiments have been conducted for ASTER/TIR in lakes such as Lake Tahoe (NV/CA), Salton Sea (CA), and Lake Kasumigaura (Japan), and in dry lakes such as Railroad Valley (NV), Alkali Lake (NV), and Coyote Lake (CA). In the present paper, 307 VC matchup data obtained by three organizations were analyzed. Overall results show that a typical difference between the at-sensor radiance acquired by onboard calibration (OBC) and that predicted by VC is about 0.5 to 1 K in the water sites and about 1 to 2 K in the land sites. The results of the responsivity analysis indicate that VC is well tracking the responsivity changes measured by OBC, though the recent discrepancy at band 10 should be investigated with more VC results. The results of the offset analysis indicate that the short term calibration (STC) which is performed at a blackbody temperature of 270 K before every Earth observation has worked normally. It is therefore concluded that the ASTER/TIR instrument has been keeping the designed accuracy (1 K for the temperature range of 270 to 340 K) since the launch.

Comparison of surface heat balance in three cities in Taiwan using Terra ASTER and Formosat-2 RSI data

Abstract In order to investigate the influences of the city scale, usage, topography, and climate on surface heat balance, the authors compared the surface heat balance for three urban areas in Taiwan, namely, Kaohsiung City, Taichung City, and Tainan City, estimated using ASTER and Formosat-2 data. The net radiation was in a similar range in all three study areas because the cities are in close proximity to each other. Tainan City released 60–70% of the sensible heat flux of the other cities because of its smaller size. Taichung City, which is located in a basin, exhibited the largest sensible heat flux, due to the radiation cooling during the night before the observation. Anthropogenic heat discharge clearly decreased the storage heat flux in certain industrial areas in Kaohsiung City and Taichung City, while the small scale urban functions moderated the variation of storage heat flux in Tainan City. These results imply that the terrain around a given city as well as the scale of urban activity significantly affect the heat balance in the cities.

Estimation of net ecosystem production in Asia using the diagnostic‐type ecosystem model with a 10 km grid‐scale resolution

The terrestrial carbon cycle in Asia is highly uncertain, and it affects our understanding of global warming. One of the important issues is the need for an enhancement of spatial resolution, since local regions in Asia are heterogeneous with regard to meteorology, land form, and land cover type, which greatly impacts the detailed spatial patterns in its ecosystem. Thus, an important goal of this study is to reasonably reproduce the heterogeneous biogeochemical patterns in Asia by enhancing the spatial resolution of the ecosystem model biosphere model integrating eco-physiological and mechanistic approaches using satellite data (BEAMS). We estimated net ecosystem production (NEP) over eastern Asia and examined the spatial differences in the factors controlling NEP by using a 10 km grid-scale approach over two different decades (2001–2010 and 2091–2100). The present and future meteorological inputs were derived from satellite observations and the downscaled Coupled Model Intercomparison Project Phase 5 (CMIP5) data set, respectively. The results showed that the present NEP in whole eastern Asia was carbon source (−214.9 TgC yr−1) and in future scenarios, the greatest positive (76.4 TgC yr−1) and least negative (−95.9 TgC yr−1) NEPs were estimated from the Representative Concentration Pathways (RCP) 6.0 and RCP8.5 scenarios, respectively. Calculated annual NEP in RCP8.5 was mostly positive in the southern part of East Asia and Southeast Asia and negative in northern and central parts of East Asia. Under the RCP scenario with higher greenhouse gases emission (RCP8.5), deciduous needleleaf and mixed forests distributed in the middle and high latitudes served as carbon source. In contrast, evergreen broadleaf forests distributed in low latitudes served as carbon sink. The sensitivity study demonstrated that the spatial tendency of NEP was largely influenced by atmospheric CO2 and temperature.

Simulation of operation of future Japanese spaceborne hyperspectral imager: HISUI

HISUI, a Japanese future spaceborne hyperspectral and multispectral imaging system, is currently being developed by Japanese Ministry of Economy, Trade, and Industry. Because of the narrow swath of the imager as well as the limits on the operation time and data downlink resource allocation, the operation strategy of HISUI should be examined thoroughly to fully utilize HISUIs earth observation capability. A software which simulates HISUIs operation is being developed for the detailed analysis of HISUIs long term operation plans. The simulation results indicate that 1) one-time priority area mapping will be completed within eight months with moderate data downlink allocation, 2) one-time global observation in a year will be possible if the allocated downlink capability is more than 250 GByte per day, 3) the nighttime volcano monitoring will not significantly affect the daytime observation if the cross track pointing only for nighttime observation is not allowed.

Moon observations for small satellite radiometric calibration

In recent years, more and more small satellites have been launched and operated for various purposes. Because of their sever restrictions of payload weight and cost, a radiometric calibration approach which does not need any special instrument has been desired. In this study, we demonstrate a radiometric calibration approach for Hodoyoshi-1, a Japanese small satellite, based on Moon observations utilizing SLENE/SP Lunar surface reflectance model. The model can simulate any satellite Moon observation considering observation geometry, and can be used for evaluating the consistency of the observed Moon brightness, which allows us to measure a time variation of a sensor sensitivity. Through Hodoyoshi-1s three Moon observations, gradual increasing in relative sensor sensitivities were confirmed.

Current status of Hyperspectral Imager Suite (HISUI) onboard International Space Station (ISS)

Hyperspectral Imager Suite (HISUI) is a future spaceborne hyperspectral Earth imaging system being developed by Japanese Ministry of Economy, Trade, and Industry (METI). HISUI will be launched and deployed on International Space Station (ISS) for three year operation from 2019. In FY2016, manufacturing and testing of HISUI Flight Model and design of HISUI Exposed Payload System were conducted. HISUI data policy and research announcement as well as synergy with other earth observing instruments onboard ISS are also being discussed.

Aster/TIR vicarious calibration activities in the last 11 years

Since March 2000, the project science team for the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) onboard NASAs Terra satellite has conducted vicarious calibration (VC) experiments periodically to verify the onboard calibration (OBC) of ASTER thermal infrared (ASTER/TIR) bands. In the present paper, 287 matchup data obtained from ten experimental sites by three organizations are analyzed. The radiance difference of OBC and VC shows almost no correlation with surface temperature and precipitable water vapor at each experimental site, but shows some dependence on the type of the experimental site. For example, the OBC-VC comparisons at Cold Springs Reservoir (NV) which is a small water body shows some bias due to the straylight effect of ASTER/TIR. The comparisons at Lake Kussharo covered by snow also show some bias maybe because of an extrapolation effect of ASTER radiometric calibration. The comparisons at Mauna Loa lava flows show a large deviation due to non-uniformity of surface temperature caused by the rough surface. Except for these cases, the results show that the latest version of radiometric calibration coefficients (version 3.×) for ASTER/TIR has been keeping the designed accuracy (1 K for the temperature range of 270 to 320 K).

Detection of thermal anomaly using Sentinel-2A data

We developed a simple algorithm for detecting hot spots using Sentinel-2A data, modifying a method for Landsat 8 data. The empirical hot spot detection equation was developed using apparent spectral reflectances at band 8a (0.87 μm) and band 12 (2.2 μm). Due to the improved spatial resolution, false detections often occur in inclined flat surfaces, such as roofs and solar panels. To avoid such false detection, we defined a new detection equation with empirical thresholds additionally using an apparent spectral reflectance at band 11 (1.6 μm) based on typical spectral characteristics of surface materials and the blackbody assumption. The proposed algorithm successfully reduced the occurrence of false detection in urban areas.