干旱区春小麦发育期反照率变化及其不对称性

反照率是影响农田热量平衡的一个关键因子,也是作物生长监测和产量估测的一个重要参数.为了研究反照率随春小麦发育期的变化规律,探讨地表反照率日变化的不对称性及其影响因子,运用辐射仪对春小麦分蘖、拔节、抽穗、灌浆及成熟等不同发育期的地表反照率日变化进行了观测.结果表明,地表反照率变化的整体趋势是随春小麦发育期的变化而先升(分蘖期至抽穗期)后降(灌浆期和成熟期).地表反照率的日变化随太阳高度角变化呈现上、下午不对称特征,当太阳高度角小于40°时,上午地表反照率要明显大于下午同样太阳高度角时的反照率,当太阳高度角大于40°时,上、下午地表反照率则逐渐对称.分析推测早晨春小麦叶片表面存在露珠是造成地表反照率日变化不对称的主要原因.研究结果为准确确定干旱区地表反照率及运用地表反照率进行作物生长临测提供一定参考依据.

Variations of surface albedo and its diurnal asymmetry at different growing stages of spring wheat in arid areas

Surface albedo greatly affects the radiation energy balance of the cropland and is a significant factor in crop growth monitoring and yields estimation. The research aimed to explore the variations of surface albedo with the transitions of different growing stages of spring wheat and analyze the diurnal asymmetry of surface albedo and its causing factor. Diurnal albedo variations were measured at different growing stages (tillering, jointing, heading, filling and maturity) of spring wheat by using a pyranometer. Results indicated that the daily mean surface albedo showed an increasing tendency during tillering to heading but decreased after heading. Surface albedos were much higher in the morning than its corresponding values of the same solar elevation angles in the afternoon when solar elevation angle was less than 40°, indicating a diurnal asymmetry of surface albedo. However, surface albedos showed less difference between forenoon and afternoon when solar elevation angle was greater than 40°. Dew droplets on the leaf surface in the morning were assumed to be the main causing factor for the diurnal albedo asymmetry of spring wheat. The study is expected to provide a reference for precisely specifying surface albedo and further monitoring crop growth using surface albedo in arid areas.