GastFarm2016_Photogrammetry_ProcessedOutputs_DEM

Project Name: Gast Farm<br> Project Location: Iowa, United States<br> Project Date: 2016 Gast Farm is a 13-hectare archaeological site located in the Mississippi River valley in southeast Iowa. Gast Farm is one of the largest and best-preserved Woodland sites in the region, with both Middle Woodland (Havana Hopewell, ca. 50 B.C.–A.D. 250) and initial Late Woodland (Weaver, ca. A.D. 350–500) deposits. Additionally, a large mound was once present, and remnants of geometric earthworks also suspected. The PIs research seeks to is to understand the interanal structure and layout of the Woodland communities at Gast Farm, which can contribute to knowledge of Middle and Late Woodland domestic and corporate-ceremonial spheres, i.e., residential as well as sustainable and symbolic communities. PI William Green collaborated with SPARC researcher Adam Barnes to produce orthorectified images and a digital elevation model (DEM) of the Gast Farm site from aerial imagery collected in 1990, using AgiSoft Photoscan. The orthophotos reveal distinct soil discolorations because the original photos were taken after the field had been disked, planted, and rained on, and only a few days after row crops (corn) had emerged. Soil discolorations indicate large-scale cultural features such as middens (dark colors) and a mound and possible geometric earthworks (light colors). The orthophotos also show a series of narrow linear discolorations exactly 10 m apart that represent the paths created during the controlled surface collection that was underway at the time the photos were taken. The DEM produced by orthophoto rectification has a 50-cm resolution, which is unfortunately is not sufficiently sensitive to detect possible mound or earthwork features after they have been leveled and plowed. This work is part of a larger 2016-2018 project at Gast Farm, which combined GIS development, aerial imagery analysis, and geophysical survey. Defining community organization, locating any subsurface traces of the mound, and determining the reality of the suspected earthwork constituted key research objectives. Over the course of the project, the Gast Farm team (1) identified the Middle Woodland (Havana-Hopewell) community plan, (2) determined no geometric earthworks were present but discovered six additional mounds, and (3) confirmed and expanded the Late Woodland (Weaver) community plan. In the process of obtaining these results, the project also accomplished several methodological advances: it (1) demonstrated the viability of magnetic gradiometry for identifying Woodland residential and mortuary features in Mississippi Valley alluvial fans, (2) showed how to incorporate legacy oblique aerial photography in a georeferenced GIS, (3) indicated the promise of drone-based photogrammetry in identifying cultural features beneath crop cover, and (4) modeled the virtual reconstruction of leveled mounds. This upload contains the digital elevation model created during the Gast Farm project in 2016. See the Index file for a list of files and folders. Photogrammetry Details: AgiSoft Photoscan<br> Operator: Adam Barnes (SPARC)<br> Imagery type: Oblique Kodachrome slides<br> Year collected: 1990<br> Camera model: Nikon SUPER COOLSCAN 5000 ED<br> Resolution: 5400 x 3700 resolution<br> Focal length: unknown<br> Pixel size: unknown<br> Precalibrated: no<br> Number of images: 24<br> Flying altitude: 987 meters<br> Ground resolution: 9.13 cm per pixel<br> Coverage area: 5.95e+05 sq meters<br> Camera stations: 23<br> Tie points: 8295<br> Projections: 17912<br> Reprojection error: 2.13 pix DEM Model Details<br> Resolution: 18.3 cm per pixel<br> Point density: 29.9607 points per sq meter Further metadata: GastFarm2016_Report/GastFarm2016_Report.pdf项目名称：盖斯特农场（Gast Farm） 项目地点：美国爱荷华州 项目日期：2016年 盖斯特农场是一处占地13公顷的考古遗址，坐落于美国爱荷华州东南部的密西西比河谷。该遗址是该区域规模最大、保存最完好的林地时期（Woodland）考古遗址之一，留存有中林地时期（Havana Hopewell，约公元前50年—公元250年）与初始晚林地时期（Weaver，约公元350年—500年）的文化堆积。此外，该遗址曾存在一座大型土丘，同时还疑似留有几何形土方工程遗迹。 本项目的研究旨在解析盖斯特农场林地时期社群的内部结构与空间布局，可为中、晚林地时期的居家生活、宗族仪式领域（即居住社群与可持续性、符号化社群）的相关研究提供认知补充。项目负责人威廉·格林（William Green）与SPARC研究人员亚当·巴恩斯（Adam Barnes）合作，基于1990年采集的航拍影像，使用AgiSoft Photoscan生成了盖斯特农场遗址的正射校正影像与数字高程模型（Digital Elevation Model, DEM）。 由于原始影像拍摄时，该农田已完成圆盘耙耕作、播种且经历降雨，仅在大田作物（玉米）出苗数天后拍摄，因此正射影像图可呈现出清晰的土壤色泽差异。土壤色泽差异可对应大型文化遗存：深色区域为垃圾堆积层（midden），浅色区域则对应土丘与疑似几何形土方工程。正射影像图还显示出一系列间距恰好为10米的窄线性色泽痕迹，对应影像拍摄时正在开展的控制性地表采集工作所留下的作业路径。 通过正射校正生成的数字高程模型分辨率为50厘米，但遗憾的是，其灵敏度不足以检测被平整、翻耕后的土丘或土方工程遗存。本工作是盖斯特农场2016—2018年大型研究项目的一部分，该项目整合了地理信息系统（Geographic Information System, GIS）开发、航拍影像分析与地球物理勘探技术。明确社群组织、定位土丘的地下痕迹、确认疑似土方工程的真实性，是该项目的核心研究目标。 项目实施期间，盖斯特农场研究团队取得了以下成果：(1) 明确了中林地时期（Havana-Hopewell）社群的空间布局；(2) 确认遗址不存在几何形土方工程，但新增发现6座土丘；(3) 完善了晚林地时期（Weaver）社群的空间布局。在取得上述成果的同时，本项目还实现了多项方法学突破：(1) 验证了磁梯度法在密西西比河谷冲积扇区域识别林地时期居住与丧葬遗存的可行性；(2) 展示了如何将遗留的倾斜航拍影像纳入地理参考GIS；(3) 证实了无人机摄影测量技术在识别作物覆盖下的文化遗存方面的应用潜力；(4) 完成了被平整土丘的虚拟重建建模。 本次上传内容为2016年盖斯特农场项目生成的数字高程模型，文件与文件夹列表详见索引文件。 摄影测量详情：AgiSoft Photoscan 操作人员：亚当·巴恩斯（SPARC） 影像类型：倾斜式柯达克罗姆（Kodachrome）幻灯片 采集年份：1990年 相机型号：尼康SUPER COOLSCAN 5000 ED 分辨率：5400×3700 焦距：未知 像素尺寸：未知 预校准状态：未预校准 影像数量：24张 飞行高度：987米 地面分辨率：9.13厘米/像素 覆盖面积：5.95×10^5平方米 相机站点数量：23个 连接点数量：8295个 投影点数量：17912个 重投影误差：2.13像素 数字高程模型详情 分辨率：18.3厘米/像素 点密度：29.9607个/平方米 其他元数据详见：GastFarm2016_Report/GastFarm2016_Report.pdf