With the increasing deployment of earth observation satellite constellations, the downlink (satellite-to-ground) capacity often limits the freshness, quality, and coverage of the imagery data available to applications on the ground. To overcome the downlink limitation, we present Earth+, a new satellite imagery compression system that, instead of compressing each image individually, pinpoints and downloads only recent imagery changes with respect to the history reference images. To minimize the amount of changes, it is critical to make reference images as fresh as possible. Earth+ enables each satellite to choose fresh reference images from not only its own history images but also past images of other satellites from an entire satellite constellation. To share reference images across satellites, Earth+ utilizes the limited capacity of the existing uplink (ground-to-satellite) by judiciously selecting and compressing reference images while still allowing accurate change detection. In short, Earth+ is the first to make reference-based compression efficient, by enabling constellation-wide sharing of fresh reference images across satellites. Our evaluation shows that Earth+ can reduce the downlink usage by a factor of 3.3 compared to state-of-the-art on-board image compression techniques while not sacrificing image quality, or using more on-board computing or storage resources, or more uplink bandwidth than currently available.

翻译：随着地球观测卫星星座的日益部署，下行链路（卫星到地面）容量常常限制了地面应用获取图像数据的新鲜度、质量和覆盖范围。为突破下行链路瓶颈，我们提出了Earth+——一种新型卫星图像压缩系统。该系统摒弃了逐幅独立压缩的传统方式，仅精确定位并下载相较于历史参考图像的最新变化。为最小化变化量，确保参考图像尽可能保持最新状态至关重要。Earth+使每颗卫星不仅可从自身历史图像中选取最新参考图，还能从整个卫星星座中其他卫星的过往图像中获取数据。为实现跨卫星的参考图像共享，Earth+通过审慎选择并压缩参考图像，在允精确变化检测的同时，充分利用现有上行链路（地面到卫星）的有限容量。简言之，Earth+首次实现了基于参考的压缩效率突破——通过跨卫星共享星座范围内最新参考图像。评估表明，与最先进的星载图像压缩技术相比，Earth+可在不牺牲图像质量、不额外消耗星载计算/存储资源或使用超出当前可用上行带宽的前提下，将下行链路使用量降低3.3倍。