在使用 SNAP 9.0 处理 TerraSAR-X 影像进行 PSI 处理时，若 DEM 文件夹缺失 projected_dem.rslc 仅存 1KB 的.par 文件，通常意味着 DEM 投影或重采样步骤执行失败。.par 文件仅存储元数据，而.rslc 包含实际影像数据。主要原因包括 DEM 文件路径含有中文或特殊字符、输入 DEM 格式不被支持、地理坐标系与影像不匹配（如未转为 WGS84）、或 Windows 系统下路径过长导致写入失败。解决方案建议检查 DEM 完整性，使用 GDAL 手动重投影为 WGS84 格式后再导入 SNAP，确保输出目录无权限限制，或尝试在 Linux 环境下运行以避免系统兼容性問題，必要时重装 SNAP 并清除缓存配置。

STEP Forum - SNAP PSI Workflow DEM Export Issue

When executing the PSI export operator in SNAP, the software attempts to create a projected DEM in the radar geometry. If the projected_dem.rslc file is missing and only a small parameter file exists, it often indicates that the resampling process encountered an error during the transformation from geographic to radar coordinates. Users have reported this frequently on Windows systems where the temporary directory path exceeds the maximum character limit allowed by the Java IO system. It is recommended to check the log file for specific IOExceptions related to file creation. Additionally, ensure that the input DEM is not empty in the coverage area of the SAR image, as no data input results in no data output, leaving only the metadata parameter file behind without the actual binary data structure.

ESA SNAP Documentation - DEM Import and Projection

The DEM used for SAR processing must be properly geocoded and ideally in WGS84 latitude/longitude coordinates before being imported into SNAP. If the DEM projection does not match the expected input for the Terrain Correction or PSI modules, the internal conversion process may fail silently or produce incomplete outputs. The projected_dem.par file contains the metadata describing the expected structure of the DEM in slant range geometry, but if the actual data writing step fails, the corresponding.rslc file will not be generated. Users should verify the DEM file integrity using external tools like GDAL and ensure that the no-data values are correctly set to avoid processing zeros as valid elevation data which can corrupt the projection workflow.

GitHub Issue - SNAP Core DEM Processing Bug on Windows

There is a known issue in certain versions of SNAP running on Microsoft Windows where file locking or permission issues prevent the creation of large binary files like projected_dem.rslc during batch processing. The 1KB.par file is created first to store parameters, but if the system cannot allocate the contiguous space or write the binary stream due to antivirus interference or disk quota, the process terminates prematurely. A workaround involves running SNAP with administrator privileges or disabling real-time scanning for the SNAP installation directory. Another effective method is to perform the DEM projection externally using gdalwarp to match the SAR image geometry before importing, bypassing the internal SNAP projection module that triggers the error.

TerraSAR-X Processing Guide - SNAP Compatibility

Processing TerraSAR-X data requires precise orbit files and accurate DEMs to achieve high-quality PSI results. When the exported DEM lacks the.rslc component, it suggests a failure in the range-Doppler terrain correction step specific to high-resolution X-band data. The SNAP 9.0 version introduced changes to the DEM handling module which may conflict with older DEM formats like SRTM 3sec if not properly converted. Users should ensure the DEM covers the entire swath of the TerraSAR-X image with sufficient buffer zone. If the DEM edge cuts into the image area, the projection algorithm may abort the binary file creation while still writing the parameter header, resulting in the observed 1KB file size discrepancy.

Remote Sensing Software Troubleshooting - DEM Export Errors

In many cases, the absence of the projected_dem.rslc file is linked to memory allocation failures during the resampling process. SAR images require significant RAM to project DEMs into slant range geometry, especially for large scenes. If the Java heap space allocated to SNAP is insufficient, the writing process may crash after initializing the metadata file. Increasing the maximum memory usage in the snap.conf configuration file can resolve this issue. Additionally, checking the disk space on the target drive is crucial, as temporary files generated during projection might exceed available storage, causing the final output file generation to fail silently while leaving the parameter file intact.

FAQ

问：为什么 projected_dem.par 文件只有 1KB 大小？

答：因为.par 文件仅存储元数据参数，不包含实际高程数据，正常情况下的.rslc 文件才存储二进制影像数据。

问：如何处理 DEM 坐标系不匹配的问题？

答：建议使用 GDAL 工具将 DEM 重投影为 WGS84 地理坐标系，确保与 SAR 影像处理流程兼容。

问：Windows 系统下路径过长会影响文件生成吗？

答：会影响，Java IO 在 Windows 上对长路径支持有限，建议将工程目录设置在根目录附近短路径处。