The most promising approach for studying soil moisture is the assimilation of observation data and computational modeling. However, there is much uncertainty in the assimilation process, which affects the assimilation...The most promising approach for studying soil moisture is the assimilation of observation data and computational modeling. However, there is much uncertainty in the assimilation process, which affects the assimilation results. This research developed a one-dimensional soil moisture assimilation scheme based on the Ensemble Kalman Filter (EnKF) and Genetic Algorithm (GA). A two-dimensional hydrologic model-Distributed Hydrology-Soil-Vegetation Model (DHSVM) was coupled with a semi-empirical backscattering model (Oh). The Advanced Synthetic Aperture Radar (ASAR) data were assimilated with this coupled model and the field observation data were used to validate this scheme in the soil moisture assimilation experiment. In order to improve the assimilation results, a cost function was set up based on the distance between the simulated backscattering coefficient from the coupled model and the observed backscattering coefficient from ASAR. The EnKF and GA were used to re-initialize and re-parameterize the simulation process, respectively. The assimilation results were compared with the free-run simulations from hydrologic model and the field observation data. The results obtained indicate that this assimilation scheme is practical and it can improve the accuracy of soil moisture estimation significantly.展开更多
利用黄土高原无定河流域1982～1991年的水文气象、土地利用、土壤质地、数字高程和NOAA-AVHRR遥感信息,建立基于土壤-植被-大气传输机理的分布式生态水文模型,模拟流域水量平衡的时空分布.研究结果发现,该流域的年平均植被指数(NDVI)的...利用黄土高原无定河流域1982～1991年的水文气象、土地利用、土壤质地、数字高程和NOAA-AVHRR遥感信息,建立基于土壤-植被-大气传输机理的分布式生态水文模型,模拟流域水量平衡的时空分布.研究结果发现,该流域的年平均植被指数(NDVI)的年际变化不明显,但NDVI最大值的年际变化显著.该流域年累计NDVI与降水年总量关系不明显,说明该流域植被的生长并不完全受控于降水总量.模拟的实际蒸散量用无定河及其岔巴沟子流域实测降水与实测径流的差值进行验证,误差小于5%.整个流域模拟时段的平均降水量为372±53 mm yr-1,实际蒸散量为334±33 mm yr-1,其中蒸腾为130±21 mm yr-1,有明显的年际波动.地表径流的年际变化相对较小.蒸散发的季节变化特征与降雨基本一致,即7、8、9月雨季高,其他月份低.降水量和实际蒸散量呈现显著的空间分异性,表现出由东南(高NDVI)向西北(低NDVI)递减的梯度差异.地表径流的空间分异亦沿东南-西北梯度变化,但高值分散在中部.以岔巴沟子流域1991年的地表覆被度为基准,发现在全流域都覆盖上某一种植被的情况下,蒸腾和土壤蒸发的变化非常明显,地表径流和实际总蒸散的变化并不显著.只有在全流域都变成荒漠情景下,实际总蒸散才显示出较明显变化(17%),表明在西北干旱半干旱区,土地利用/覆被变化对水量平衡的影响非常复杂.展开更多
为模拟详细的温度分布信息,进一步理解地表能量平衡过程,提高植被冠层温度反演精度,根据土壤阴影表面和光照表面的热源和蒸发速率的差异,扩展了CU P ID模型,实现了光照和阴影土壤组分温度分布模拟。采用实测数据分别对冬小麦和夏玉米冠...为模拟详细的温度分布信息,进一步理解地表能量平衡过程,提高植被冠层温度反演精度,根据土壤阴影表面和光照表面的热源和蒸发速率的差异,扩展了CU P ID模型,实现了光照和阴影土壤组分温度分布模拟。采用实测数据分别对冬小麦和夏玉米冠层下的土壤组分温度进行了模拟和验证。在冬小麦地,模拟光照和阴影土壤温度绝对差值为2.8 K和2.4K,平均差值为-1.5 K和-0.7 K;在夏玉米地,模拟与实测温度绝对偏差为3.8 K左右,平均偏差为-0.5 K。总体来说,模拟与实测数据吻合较好,说明扩展模型能够较为真实地反映土壤组分温度分布及其变化。扩展模型可在组分温度反演和农业旱情监测等领域得到应用。展开更多
基金Under the auspices of Major State Basic Research Development Program of China (973 Program) (No. 2007CB714400)the Program of One Hundred Talents of the Chinese Academy of Sciences (No. 99T3005WA2)
文摘The most promising approach for studying soil moisture is the assimilation of observation data and computational modeling. However, there is much uncertainty in the assimilation process, which affects the assimilation results. This research developed a one-dimensional soil moisture assimilation scheme based on the Ensemble Kalman Filter (EnKF) and Genetic Algorithm (GA). A two-dimensional hydrologic model-Distributed Hydrology-Soil-Vegetation Model (DHSVM) was coupled with a semi-empirical backscattering model (Oh). The Advanced Synthetic Aperture Radar (ASAR) data were assimilated with this coupled model and the field observation data were used to validate this scheme in the soil moisture assimilation experiment. In order to improve the assimilation results, a cost function was set up based on the distance between the simulated backscattering coefficient from the coupled model and the observed backscattering coefficient from ASAR. The EnKF and GA were used to re-initialize and re-parameterize the simulation process, respectively. The assimilation results were compared with the free-run simulations from hydrologic model and the field observation data. The results obtained indicate that this assimilation scheme is practical and it can improve the accuracy of soil moisture estimation significantly.
文摘利用黄土高原无定河流域1982～1991年的水文气象、土地利用、土壤质地、数字高程和NOAA-AVHRR遥感信息,建立基于土壤-植被-大气传输机理的分布式生态水文模型,模拟流域水量平衡的时空分布.研究结果发现,该流域的年平均植被指数(NDVI)的年际变化不明显,但NDVI最大值的年际变化显著.该流域年累计NDVI与降水年总量关系不明显,说明该流域植被的生长并不完全受控于降水总量.模拟的实际蒸散量用无定河及其岔巴沟子流域实测降水与实测径流的差值进行验证,误差小于5%.整个流域模拟时段的平均降水量为372±53 mm yr-1,实际蒸散量为334±33 mm yr-1,其中蒸腾为130±21 mm yr-1,有明显的年际波动.地表径流的年际变化相对较小.蒸散发的季节变化特征与降雨基本一致,即7、8、9月雨季高,其他月份低.降水量和实际蒸散量呈现显著的空间分异性,表现出由东南(高NDVI)向西北(低NDVI)递减的梯度差异.地表径流的空间分异亦沿东南-西北梯度变化,但高值分散在中部.以岔巴沟子流域1991年的地表覆被度为基准,发现在全流域都覆盖上某一种植被的情况下,蒸腾和土壤蒸发的变化非常明显,地表径流和实际总蒸散的变化并不显著.只有在全流域都变成荒漠情景下,实际总蒸散才显示出较明显变化(17%),表明在西北干旱半干旱区,土地利用/覆被变化对水量平衡的影响非常复杂.
