OPTICAL THICKNESS DATA: BRUEGGE (FIFE)

The NIPS and Reagan Sunphotometer Optical Thickness study compared various ground and image-based techniques used to characterize the atmosphere. These data are used to remove atmospheric absorption and scattering from remote sensing scenes so that surface parameters can be retrieved. An evaluation of the effects of uncorrected atmospheric absorption and scattering on various vegetation indices and subsequent biophysical parameter estimations was also undertaken. These data can also be used to derive aerosol size distribution (King et al., 1978) and thereby estimate the phase function. Aerosol optical depths were recorded at various locations within the FIFE site. A Normal Incident Pyrheliometer (NIP) and a Reagan sunphotometer was used to collect data during the IFCs. These data showed that daily averages span a range of 0.05 to 0.28 in the mid-visible wavelength (Bruegge et al., 1992a). Diurnal variations were recorded. The afternoon optical depths are greater than those of the morning by as much as 0.07. These data are analyzed using the Langley technique. Rayleigh optical depth is subtracted, and aerosol, ozone, and water vapor abundance's simultaneously measured. In retrieving ozone, a Junge aerosol model is assumed, thus, the natural log of aerosol optical depth is linear with wavelength (Bruegge et al., 1992a). This contrasts with other experimental approaches used by investigators in which an ozone abundance is assumed (Halthore and Markham 1992). This approach allows measurement of aerosol, but is limited by the accuracy of the ozone data.

本数据集为直射日射强度计（Normal Incident Pyrheliometer, NIP）与里根太阳光度计的光学厚度研究数据，对比了多种用于大气特性表征的地面与成像技术。此类数据可用于剔除遥感场景中的大气吸收与散射干扰，以反演获取地表参数。研究同时评估了未校正的大气吸收与散射对多种植被指数及后续生物物理参数反演的影响。本数据集还可用于推导气溶胶粒径分布（King等，1978），进而估算气溶胶相函数。研究在FIFE试验区内多个点位记录了气溶胶光学厚度：在IFCs观测期间，采用NIP与里根太阳光度计开展数据采集。数据显示，中可见波段的日平均光学厚度介于0.05至0.28之间（Bruegge等，1992a）。研究同步记录了光学厚度的日变化特征：午后光学厚度较上午最大可高出0.07。上述数据采用兰利法（Langley technique）进行分析：首先扣除瑞利光学厚度，同时同步测量气溶胶、臭氧与水汽含量。在臭氧反演环节，研究采用容格气溶胶模型（Junge aerosol model）假设，即气溶胶光学厚度的自然对数与波长呈线性相关（Bruegge等，1992a）。该方法与其他研究者采用的实验路径存在显著差异——后者通常预先假定臭氧含量（Halthore与Markham，1992）。此方法虽可实现气溶胶参数测量，但受限于臭氧数据的精度。