Detection and Quantification of Snow Algae with an Airborne Imaging Spectrometer

We describe spectral reflectance measurements of snow containing the snow alga Chlamydomonas nivalis and a model to retrieve snow algal concentrations from airborne imaging spectrometer data. Because cells of C. nivalis absorb at specific wavelengths in regions indicative of carotenoids (astaxanthin esters, lutein, β-carotene) and chlorophylls a and b, the spectral signature of snow containing C. nivalis is distinct from that of snow without algae. The spectral reflectance of snow containing C. nivalis is separable from that of snow without algae due to carotenoid absorption in the wavelength range from 0.4 to 0.58 μm and chlorophyll a and b absorption in the wavelength range from 0.6 to 0.7 μm. The integral of the scaled chlorophyll a and b absorption feature (I(0.68)) varies with algal concentration (C(a)). Using the relationship C(a) = 81019.2 I(0.68) + 845.2, we inverted Airborne Visible Infrared Imaging Spectrometer reflectance data collected in the Tioga Pass region of the Sierra Nevada in California to determine algal concentration. For the 5.5-km(2) region imaged, the mean algal concentration was 1,306 cells ml(−1), the standard deviation was 1,740 cells ml(−1), and the coefficient of variation was 1.33. The retrieved spatial distribution was consistent with observations made in the field. From the spatial estimates of algal concentration, we calculated a total imaged algal biomass of 16.55 kg for the 0.495-km(2) snow-covered area, which gave an areal biomass concentration of 0.033 g/m(2).

本研究阐述了含有雪衣藻（Chlamydomonas nivalis）的积雪的光谱反射率测量方法，以及一种从航空成像光谱仪数据中反演雪藻浓度的模型。由于雪衣藻细胞在类胡萝卜素（虾青素酯、叶黄素、β-胡萝卜素）与叶绿素a、b的特征吸收波段处具有特异性吸收，因此含有雪衣藻的积雪光谱特征与无藻积雪存在显著差异。由于类胡萝卜素在0.4~0.58 μm波长范围内的吸收作用，以及叶绿素a、b在0.6~0.7 μm波长范围内的吸收作用，含有雪衣藻的积雪光谱反射率可与无藻积雪的光谱反射率有效区分。归一化处理后的叶绿素a、b吸收特征的积分值（I(0.68)）随雪藻浓度C(a)变化。利用公式C(a) = 81019.2 × I(0.68) + 845.2，我们对采集自美国加利福尼亚州内华达山脉提奥加山口（Tioga Pass）区域的航空可见光/红外成像光谱仪反射率数据进行反演，以获取雪藻浓度。在此次成像的5.5 km²研究区域内，雪藻平均浓度为1306 个·mL⁻¹，标准差为1740 个·mL⁻¹，变异系数为1.33。反演得到的雪藻空间分布与野外实地观测结果一致。基于雪藻浓度的空间估算结果，我们计算得出此次成像的0.495 km²积雪覆盖区域内总雪藻生物量为16.55 kg，对应的单位面积生物量浓度为0.033 g/m²。