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14Conditional simulation with sparse sensorsTo monitor the condition of bridges, sensors measure the loadings and responses of the structure. These sensors commonly include thermometers and pyranometers to measure or simulate the temperature of the bridge, anemometers to measure wind speed, accelerometers to measure vibrations, strain gauges and displacement transducers to measure deformation or displacement of structures, video cameras to detect vibration using videogrammetry, optical fibre sensors to measure strain and temperature, and global navigation satellite system sensors to measure structural movement.One limitation of traditional SHM is the limited number of sensors that it can accommodate. As long bridges can span over 20 kilometres, installing sensors along their entire lengths is impractical due to the exorbitant costs and the overwhelming volume of data generated. As a result, a small number of sensors are strategically placed at specific points on a bridge. This limited sensor distribution restricts traditional SHM to rough estimates of load and response between these sensor points.To accurately reconstruct the load and response profile along an entire bridge, the team developed a conditional simulation method. %u201cSignals from various sensor points are analysed to simulate factors such as wind speed, seismic motion, temperature and traffic load at every point along a bridge using mathematical frameworks such as the coherence model and cross spectral density,%u201d says Prof. Xia. Despite the small number of sensors, the system accurately reconstructs the load and response accurately across the entire length of a bridge.FOREVER YOUNG