Seasonal Comparisons of Himawari-8 AHI and MODIS Vegetation Indices over Latitudinal Australian Grassland Sites
The Advanced Himawari Imager (AHI) on board the Himawari-8 geostationary (GEO) satellite offers comparable spectral and spatial resolutions as low earth orbiting (LEO) sensors such as the Moderate Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS) sens...
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MDPI AG
2020-08-01
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| Series: | Remote Sensing |
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| Online Access: | https://www.mdpi.com/2072-4292/12/15/2494 |
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| author | Ngoc Nguyen Tran Alfredo Huete Ha Nguyen Ian Grant Tomoaki Miura Xuanlong Ma Alexei Lyapustin Yujie Wang Elizabeth Ebert |
| author_facet | Ngoc Nguyen Tran Alfredo Huete Ha Nguyen Ian Grant Tomoaki Miura Xuanlong Ma Alexei Lyapustin Yujie Wang Elizabeth Ebert |
| author_sort | Ngoc Nguyen Tran |
| collection | DOAJ |
| description | The Advanced Himawari Imager (AHI) on board the Himawari-8 geostationary (GEO) satellite offers comparable spectral and spatial resolutions as low earth orbiting (LEO) sensors such as the Moderate Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS) sensors, but with hypertemporal image acquisition capability. This raises the possibility of improved monitoring of highly dynamic ecosystems, such as grasslands, including fine-scale phenology retrievals from vegetation index (VI) time series. However, identifying and understanding how GEO VI temporal profiles would be different from traditional LEO VIs need to be evaluated, especially with the new generation of geostationary satellites, with unfamiliar observation geometries not experienced with MODIS, VIIRS, or Advanced Very High Resolution Radiometer (AVHRR) VI time series data. The objectives of this study were to investigate the variations in AHI reflectances and normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), and two-band EVI (EVI2) in relation to diurnal phase angle variations, and to compare AHI VI seasonal datasets with MODIS VIs (standard and sun and view angle-adjusted VIs) over a functional range of dry grassland sites in eastern Australia. Strong NDVI diurnal variations and negative NDVI hotspot effects were found due to differential red and NIR band sensitivities to diurnal phase angle changes. In contrast, EVI and EVI2 were nearly insensitive to diurnal phase angle variations and displayed nearly flat diurnal profiles without noticeable hotspot influences. At seasonal time scales, AHI NDVI values were consistently lower than MODIS NDVI values, while AHI EVI and EVI2 values were significantly higher than MODIS EVI and EVI2 values, respectively. We attributed the cross-sensor differences in VI patterns to the year-round smaller phase angles and backscatter observations from AHI, in which the sunlit canopies induced a positive EVI/ EVI2 response and negative NDVI response. BRDF adjustments of MODIS VIs to solar noon and to the oblique view zenith angle of AHI resulted in strong cross-sensor convergence of VI values (R<sup>2</sup> > 0.94, mean absolute difference <0.02). These results highlight the importance of accounting for cross-sensor observation geometries for generating compatible AHI and MODIS annual VI time series. The strong agreement found in this study shows promise in cross-sensor applications and suggests that a denser time series can be formed through combined GEO and LEO measurement synergies. |
| first_indexed | 2024-03-10T18:00:28Z |
| format | Article |
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| issn | 2072-4292 |
| language | English |
| last_indexed | 2024-03-10T18:00:28Z |
| publishDate | 2020-08-01 |
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| spelling | doaj.art-ecf3f638cf7b4e56be2eabd81b78d4f72023-11-20T08:58:22ZengMDPI AGRemote Sensing2072-42922020-08-011215249410.3390/rs12152494Seasonal Comparisons of Himawari-8 AHI and MODIS Vegetation Indices over Latitudinal Australian Grassland SitesNgoc Nguyen Tran0Alfredo Huete1Ha Nguyen2Ian Grant3Tomoaki Miura4Xuanlong Ma5Alexei Lyapustin6Yujie Wang7Elizabeth Ebert8School of Life Science, University of Technology Sydney, Ultimo, NSW 2007, AustraliaSchool of Life Science, University of Technology Sydney, Ultimo, NSW 2007, AustraliaSchool of Life Science, University of Technology Sydney, Ultimo, NSW 2007, AustraliaBureau of Meteorology, Docklands, VIC 3008, AustraliaDepartment of Natural Resources and Environmental Management, University of Hawaii at Manoa, Honolulu, HI 96822, USASchool of Earth and Environmental Sciences, Lanzhou University, Lanzhou, Gansu 730000, ChinaNASA Goddard Space Flight Center, Greenbelt, MD 20771, USANASA Goddard Space Flight Center, Greenbelt, MD 20771, USABureau of Meteorology, Docklands, VIC 3008, AustraliaThe Advanced Himawari Imager (AHI) on board the Himawari-8 geostationary (GEO) satellite offers comparable spectral and spatial resolutions as low earth orbiting (LEO) sensors such as the Moderate Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS) sensors, but with hypertemporal image acquisition capability. This raises the possibility of improved monitoring of highly dynamic ecosystems, such as grasslands, including fine-scale phenology retrievals from vegetation index (VI) time series. However, identifying and understanding how GEO VI temporal profiles would be different from traditional LEO VIs need to be evaluated, especially with the new generation of geostationary satellites, with unfamiliar observation geometries not experienced with MODIS, VIIRS, or Advanced Very High Resolution Radiometer (AVHRR) VI time series data. The objectives of this study were to investigate the variations in AHI reflectances and normalized difference vegetation index (NDVI), enhanced vegetation index (EVI), and two-band EVI (EVI2) in relation to diurnal phase angle variations, and to compare AHI VI seasonal datasets with MODIS VIs (standard and sun and view angle-adjusted VIs) over a functional range of dry grassland sites in eastern Australia. Strong NDVI diurnal variations and negative NDVI hotspot effects were found due to differential red and NIR band sensitivities to diurnal phase angle changes. In contrast, EVI and EVI2 were nearly insensitive to diurnal phase angle variations and displayed nearly flat diurnal profiles without noticeable hotspot influences. At seasonal time scales, AHI NDVI values were consistently lower than MODIS NDVI values, while AHI EVI and EVI2 values were significantly higher than MODIS EVI and EVI2 values, respectively. We attributed the cross-sensor differences in VI patterns to the year-round smaller phase angles and backscatter observations from AHI, in which the sunlit canopies induced a positive EVI/ EVI2 response and negative NDVI response. BRDF adjustments of MODIS VIs to solar noon and to the oblique view zenith angle of AHI resulted in strong cross-sensor convergence of VI values (R<sup>2</sup> > 0.94, mean absolute difference <0.02). These results highlight the importance of accounting for cross-sensor observation geometries for generating compatible AHI and MODIS annual VI time series. The strong agreement found in this study shows promise in cross-sensor applications and suggests that a denser time series can be formed through combined GEO and LEO measurement synergies.https://www.mdpi.com/2072-4292/12/15/2494Himawari-8AHIMODISphase anglegrasslandNDVI |
| spellingShingle | Ngoc Nguyen Tran Alfredo Huete Ha Nguyen Ian Grant Tomoaki Miura Xuanlong Ma Alexei Lyapustin Yujie Wang Elizabeth Ebert Seasonal Comparisons of Himawari-8 AHI and MODIS Vegetation Indices over Latitudinal Australian Grassland Sites Remote Sensing Himawari-8 AHI MODIS phase angle grassland NDVI |
| title | Seasonal Comparisons of Himawari-8 AHI and MODIS Vegetation Indices over Latitudinal Australian Grassland Sites |
| title_full | Seasonal Comparisons of Himawari-8 AHI and MODIS Vegetation Indices over Latitudinal Australian Grassland Sites |
| title_fullStr | Seasonal Comparisons of Himawari-8 AHI and MODIS Vegetation Indices over Latitudinal Australian Grassland Sites |
| title_full_unstemmed | Seasonal Comparisons of Himawari-8 AHI and MODIS Vegetation Indices over Latitudinal Australian Grassland Sites |
| title_short | Seasonal Comparisons of Himawari-8 AHI and MODIS Vegetation Indices over Latitudinal Australian Grassland Sites |
| title_sort | seasonal comparisons of himawari 8 ahi and modis vegetation indices over latitudinal australian grassland sites |
| topic | Himawari-8 AHI MODIS phase angle grassland NDVI |
| url | https://www.mdpi.com/2072-4292/12/15/2494 |
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