Neeti N, Kennedy R
Department of Natural Resources, TERI University, New Delhi, India.
College of Earth, Ocean, Atmospheric Sciences, Oregon State University, Corvallis, OR USA.
Carbon Balance Manag. 2016 Aug 26;11(1):19. doi: 10.1186/s13021-016-0060-y. eCollection 2016 Dec.
As Earth observation satellite data proliferate, so too do maps derived from them. Even when two co-located maps are produced with low overall error, the spatial distribution of error may not be the same. Increasingly, methods will be needed to understand differences among purportedly similar products. For this study, we have used the four aboveground biomass (AGB) maps for conterminous US generated under NASA's Carbon Monitoring System. We have developed systematic approach to (1) assess both the absolute accuracy of individual maps and assess the spatial patterns of agreement among maps, and (2) investigate potential causes of the spatial structure of agreement among maps to gain insight into reliability of methodological choices in map making.
The comparison of the four biomass maps with FIA based total biomass estimates at national scale suggest that all the maps have higher biomass estimate compared to FIA. When the four maps were compared among each other, the result shows that the maps S and K have more similar spatial structure whereas the maps K and W have more similar absolute values. Although the maps K and W were generated using completely different methodological workflow, they agree remarkably. All the maps did well in the dominant forest type with maximum agreement between them. The comparison of difference between maps S and K with regional maps suggests that these maps were able to capture the disturbance and not so much regrowth pattern.
The study provides a comprehensive systematic approach to compare and evaluate different real data products using examples of four AGB maps. Although ostensibly the four maps map the same variable, they have different spatial distribution at different scale. Except the 2003 map, one can use other maps at the coarser spatial resolution. Finally, the disparate information available through different maps indicates a need for a temporal framework for consistent monitoring of carbon stock at national scale.
随着地球观测卫星数据的激增，从中衍生出的地图数量也在增加。即使两张在同一地点生成的地图总体误差较小，误差的空间分布也可能不同。因此，越来越需要一些方法来理解看似相似的产品之间的差异。在本研究中，我们使用了美国国家航空航天局碳监测系统生成的美国本土的四张地上生物量（AGB）地图。我们开发了一种系统方法来：（1）评估每张地图的绝对精度，并评估地图之间的空间一致性模式；（2）研究地图之间一致性空间结构的潜在原因，以深入了解制图方法选择的可靠性。
在国家尺度上，将这四张生物量地图与基于森林资源清查（FIA）的总生物量估计值进行比较，结果表明所有地图的生物量估计值都高于FIA。当将这四张地图相互比较时，结果显示地图S和K具有更相似的空间结构，而地图K和W具有更相似的绝对值。尽管地图K和W是使用完全不同的方法流程生成的，但它们的一致性非常显著。所有地图在主要森林类型方面表现良好，它们之间的一致性最高。将地图S和K之间的差异与区域地图进行比较表明，这些地图能够捕捉到干扰情况，但对再生模式的捕捉能力较弱。
本研究提供了一种全面的系统方法，以四张AGB地图为例来比较和评估不同的真实数据产品。尽管表面上这四张地图绘制的是相同变量，但它们在不同尺度上具有不同的空间分布。除了2003年的地图外，人们可以在较粗的空间分辨率下使用其他地图。最后，通过不同地图获得的不同信息表明，需要一个时间框架来在国家尺度上对碳储量进行持续监测。
