Assessing Lava Flow Subpixel Surface Roughness and Particle Size Distribution for Improved Thermal Inertia Interpretations
Assessing Lava Flow Subpixel Surface Roughness and Particle Size Distribution for Improved Thermal Inertia Interpretations
复制标题
评估熔岩流子像素表面粗糙度和粒度分布以改进热惯性解释
作者：
C. Simurda;M. Ramsey;S. Scheidt
表观热惯量（ATI）是一种基于遥感的热物理近似，用于估计表面特性，如颗粒大小或土壤水分，但如果假设均匀的表面材料，则会过度简化。地质表面实际上包含多种类型的材料，这些材料由数字图像中的混合像素表示，可以显著影响导出的热响应。因此，当前的表面均匀性假设可能导致错误的计算。为了确定这些混合粒度表面如何影响ATI，在Mono Domes（加州）的North Coulee流纹岩流进行了多仪器、多光谱研究。该水流成分均匀，颗粒大小从淤泥大小到卵石，使其成为了解颗粒大小分布和ATI之间关系的理想位置。结合实地收集的样品、全球定位系统和摄影测量数据，对空间分辨率不断提高的轨道传感器多光谱数据进行了分析。根据WorldView-2可见光数据和实地观测，将表面颗粒尺寸特征分为三大类（细、中、粗）。广泛的类别进行了验证，使用三维点云来自结构从运动（SfM）的方法，使用现场照片。导出ATI像素内每个类别的面积百分比，以用相应的ATI值填充查找表（LUT），从而量化混合像素的效果。正如预期的那样，较低的ATI值以细颗粒（沙子和灰尘）为主，然而，具有最高值的表面主要是中等大小的鹅卵石。具有粗粒度的高面积百分比的像素显示中间ATI值，这表明自阴影或细颗粒的捕获降低了ATI值。或者，如现场数据所示，大多数中等粒度的区域具有较少的阴影和较小材料的有效垂直分选，从而留下指示主要粒度的热衍生响应。这项研究表明，一个统一的属性假设可能会导致错误的热模拟，特别是在表面上的巨石和大颗粒尺寸的百分比高。未来对地球或其他行星表面的热物理研究可以大大受益于多传感器方法与更高空间分辨率的可见数据集的结合。
Apparent thermal inertia (ATI) is a remote sensing-based thermophysical approximation used to estimate surface properties such as particle size or soil moisture, but is subject to oversimplifications if uniform surface materials are assumed. Geological surfaces realistically contain multiple types of materials that are represented by mixed pixels in a digital image that can dramatically affect the derived thermal response. Thus, the current surface uniformity assumption can lead to erroneous calculations. To define how these mixed particle size surfaces affect ATI, a multi-instrument, multi-spectral study was conducted at the North Coulee rhyolite flow, Mono Domes (California). This flow is compositionally homogenous with particle sizes ranging from silt size to boulders, making it an ideal location to understand the relationship between particle size distributions and ATI. Multispectral data from orbital sensors with increasing spatial resolutions were analyzed in combination with samples, GPS, and photogrammetry data collected in the field. The surface particle size characteristics divided into three broad categories (fine, moderate, and coarse) were mapped based on WorldView-2 visible data and field observations. Broad categories were validated using a 3-dimensional point cloud derived from structure-from-motion (SfM) methods using field photographs. The areal percentage of each category within an ATI pixel was derived to populate a lookup table (LUT) with the corresponding ATI values to quantify the effect of mixed pixels. Lower ATI values are dominated by fine particles (sand and dust) as expected, however, surfaces with the highest values were predominately moderate-sized cobbles. Pixels with a high areal percentage of coarse sizes display an intermediate ATI value, suggesting that either self-shadowing or trapping of fines lowers the ATI value. Alternatively, areas with a majority of moderate particle sizes have less shadowing and efficient vertical sorting of smaller material, as seen in field data, leaving a thermal derived response indicative of the dominating particle size. This study demonstrates how a uniform property assumption can cause erroneous derived thermal modeling, particularly over surfaces with a high percentage of boulders and large particle sizes. Future thermophysical studies of Earth or other planetary surfaces can greatly benefit from a multi-sensor approach combined with a higher spatial resolution visible dataset.