Delta-X: UAVSAR L3 Water Level Changes, MRD, Louisiana, 2021

This dataset contains georeferenced InSAR-derived water level change maps for Delta-X flight lines acquired during the spring (2021-03-27 to 2021-04-18) and fall (2021-09-03 to 2021-09-13) deployments. Water-level change observations are provided throughout wetlands of the Atchafalaya and Terrebonne Basins, in Southern Louisiana, USA, within the Mississippi River Delta (MRD). The data were collected by Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR), a polarimetric L-band synthetic aperture radar flown on the NASA Gulfstream-III (C20) aircraft as part of the Delta-X campaign. Water surface elevations were measured on multiple flights at 30-minute intervals. There are three types of gridded products available: temporalcoherence (which provide an index measuring quality of phase unwrapping ranging from 0 (poor) to 1 (correctly unwrapped)), waterlevelchange in centimeters (which provide cumulative changes in water levels at approximately 30-minute intervals), and waterlevelchange_ramp in centimeters (which provide a 2-dimensional linear trend in water-level estimates not related to changing water levels). The water-level change maps were estimated using the phase unwrapping corrected interferograms generated for nearest-neighbor (NN), NN+1, and NN+2 pairs for data acquired within a single flight (one day). This analysis was done for all flight lines. Water level changes are relative to the first sampling flight for that study area. Data quality was assessed by comparing water elevation estimates with data from in situ water level gauges throughout the study area. A series of quality assurance masks of troposphere-induced phase delay regions were generated for all SAR acquisition dates using a weather feature matching algorithm.

本数据集包含地理参考的合成孔径雷达干涉测量（InSAR）生成的水位变化地图，对应美国路易斯安那州南部密西西比河三角洲（MRD）内阿查法拉亚盆地与特尔博恩盆地的湿地区域，数据采集自Delta-X项目的飞行航线，分为春季（2021-03-27至2021-04-18）与秋季（2021-09-03至2021-09-13）两次野外部署。
该数据由无人飞行器合成孔径雷达（UAVSAR）采集，这是一款搭载于美国国家航空航天局（NASA）湾流III（C20）飞机的极化L波段合成孔径雷达，作为Delta-X科考项目的组成部分完成数据获取。
水面高程在多次飞行任务中以30分钟为间隔进行观测。本次公开三类网格化产品：
1. 时间相干性（temporal coherence）：取值范围为0（解缠质量极差）至1（相位解缠完全正确），用于表征相位解缠操作的质量指数；
2. 厘米级水位变化（waterlevelchange）：对应约30分钟间隔的累积水位变化量；
3. 厘米级斜坡水位变化（waterlevelchange_ramp）：表征水位估算结果中与实际水位变动无关的二维线性趋势。
本次水位变化地图基于单日单架次飞行内采集的近邻（NN）、NN+1及NN+2配对干涉图，经相位解缠校正后生成，覆盖全部飞行航线。水位变化量以对应研究区域首次采样飞行的观测值作为相对基准。
数据质量通过将水位高程估算值与研究区内原位水位计的实测数据进行对比完成评估。此外，研究团队利用气象特征匹配算法，为所有合成孔径雷达（SAR）采集日期生成了一系列针对对流层引发的相位延迟区域的质量保障掩码。