Early validation study of the photochemical reflectance index (PRI) and the normalized difference vegetation index (NDVI) derived from the GCOM-C satellite in Mongolian grasslands
Early validation study of the photochemical reflectance index (PRI) and the normalized difference vegetation index (NDVI) derived from the GCOM-C satellite in Mongolian grasslands
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DOI：
10.1080/01431161.2022.2128923
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发表时间：
2022-07
影响因子：
3.4
通讯作者：
Undrakh Bayarsaikhan;T. Akitsu;K. Tachiiri;Taiga Sasagawa;T. Nakano;Bayarsaikhan Uudus;K. Nasahara
中科院分区：
文献类型：
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作者：
Undrakh Bayarsaikhan;T. Akitsu;K. Tachiiri;Taiga Sasagawa;T. Nakano;Bayarsaikhan Uudus;K. Nasahara
2017年启动的全球变化观测任务-气候（GCOM-C）具有与光化学反射指数（PRI）定义相匹配的合适波段。它还具有归一化差异植被指数（NDVI）的波段。PRI具有独特的能力，可以检测由过度光照和干旱引起的植物胁迫。然而，没有中等分辨率的卫星有适合PRI的波段，在定义中需要绿色光的两个窄带。在这项研究中，我们进行了早期验证研究的PRI和NDVI来自GCOM-C卫星，并证明了蒙古草原的准确性和特点。蒙古草原（干旱草原）在高原上广泛分布，因此适合卫星验证。由于蒙古草原夏季降水量少，水分胁迫严重，特别适合PRI验证。因此，我们在蒙古的三个研究中心开展了实地活动。在这项研究中，我们发现了PRI的季节性模式，这表明有可能检测到植被的水分胁迫，这是必要的信息，知情的草地管理。然而，卫星派生的PRI和原位PRI之间的相关性是负的，因为GCOM-C PRI依赖于稀疏植被的土壤水分。由于PRI依赖于一天中快速变化的光照和土壤湿度，因此需要更精确的现场和卫星观测同步。另一方面，我们发现，从GCOM-C推导的NDVI是高度准确的：卫星推导的NDVI和原位NDVI之间的相关系数（R）为0.988（RMSE=0.052）。GCOM-C NDVI在精度、空间分辨率和频率方面与MODIS NDVI有足够的相似性。例如，我们证明了GCOM-C NDVI可以检测物候与相同或更好的精度比MODIS NDVI。我们还证明了它们的区别：稀疏植被的土壤水分依赖性。GCOM-C NDVI对土壤水分的依赖性较小，因此与MODIS NDVI相比，GCOM-C NDVI能够更好地对稀疏草地的植被和非植被进行分类。
ABSTRACT The Global Change Observation Mission-Climate (GCOM-C), launched in 2017, has suitable bands matching the photochemical reflectance index (PRI) definition. It also has the bands for the normalized difference vegetation index (NDVI). The PRI has a unique capability to detect plant stress caused by excessive light and drought. However, no moderate-resolution satellites had suitable bands for the PRI, requiring two narrow bands in green light in the definition. In this study, we conducted the early validation study of PRI and NDVI derived from the GCOM-C satellite and demonstrated those accuracies and characteristics in Mongolian grassland. The Mongolian Steppes (dry grasslands) are widely distributed on the plateau and therefore suitable for satellite validation. It is particularly suitable for the PRI validation because Mongolian grasslands have water stress due to the small amount of precipitation in summer. Therefore, we carried out field campaigns at three study sites in Mongolia. In this study, we found the seasonal pattern of PRI suggesting the potential to detect the water stress of vegetation, which is essential information for informed management of the grasslands. However, the correlation between the satellite-derived PRI and the in-situ PRI was negative because of the dependence of GCOM-C PRI on the soil moisture at sparse vegetation. For the accuracy assessment of PRI, which depends on rapidly changing light and soil moisture in a day, more exact synchronization of in-situ and satellite observation is required. On the other hand, we found that the NDVI derived from GCOM-C was highly accurate: The correlation coefficient (R) between the satellite-derived NDVI and the in-situ NDVI was 0.988 (RMSE=0.052). GCOM-C NDVI has enough similarities with MODIS NDVI in terms of accuracy, spatial resolution, and frequency. For example, we demonstrated that GCOM-C NDVI could detect the phenology with the same or better accuracy than MODIS NDVI. We also demonstrated their difference: the soil moisture dependence in sparse vegetation. The less dependency of GCOM-C NDVI on the soil moisture leads to a better classification of vegetation and non-vegetation in the sparse grassland than MODIS NDVI.