ABSTRACT

Soil emissivity of Arctic regions is a key parameter for assessing surface properties from microwave brightness temperature (Tb) measurements. Particularly in winter, frozen soil permittivity and roughness are two poorly characterized unknowns that must be considered. Here, we show that after removing snow, the 3D soil roughness can be accurately inferred from in-situ photogrammetry using Structure from Motion (SfM). We focus on using SfM techniques to provide accurate roughness measurements and improve emissivity models parametrization of frozen arctic soil for microwave applications. Validation was performed from ground-based radiometric measurements at 19 and 37 GHz using three different soil emission models: the Wegmüller and Mätzler [1999, TGRS] model (Weg99), the Wang and Choudhury [1981, JGR] model (QNH), and a geometrical optics model (Geo Optics). Measured and simulated brightness temperatures over different tundra and rock sites in the Canadian High Arctic show that Weg99, parametrized with SfM-based roughness and optimized permittivity $(\epsilon )$, yielded an RMSE of 3.1 K ($R^2=0.71$) for all frequencies and polarizations. Our SfM based approach allowed us to measure roughness with 0.1 mm accuracy at 55 locations of different land cover type using a digital camera and metal plates of know dimensions.

摘要

北极地区的土壤发射率是通过微波亮温 (Tb) 测量评估地表特性的关键参数。特别是在冬季，冻土介电常数和粗糙度是必须考虑的两个特征不佳的未知数。在这里，我们展示了在去除雪之后，可以使用结构来自运动 (SfM) 从原位摄影测量准确推断出 3D 土壤粗糙度。我们专注于使用 SfM 技术来提供精确的粗糙度测量，并改进用于微波应用的冷冻北极土壤的发射率模型参数化。使用三种不同的土壤发射模型对 19 GHz 和 37 GHz 的地面辐射测量进行了验证：Wegmüller 和 Mätzler [1999, TGRS] 模型 (Weg99)、Wang 和 Choudhury [1981, JGR] 模型 (QNH)、和几何光学模型（Geo Optics）。在加拿大高北极地区不同苔原和岩石地点测量和模拟的亮温表明，Weg99，使用基于 SfM 的粗糙度和优化的介电常数参数化$(\epsilon )$, 产生了 3.1 K (${\mathrm{电阻}}^2=0.71$) 适用于所有频率和极化。我们基于 SfM 的方法使我们能够使用数码相机和已知尺寸的金属板在 55 个不同土地覆盖类型的位置以 0.1 毫米的精度测量粗糙度。