||Satellite remote sensing provides a synoptic view of surface ocean properties. AVHRR sea surface temperature, AVHRR visible and near-frared reflectances, and SeaWiFS or OCTS ocean color reveals variations in surface water masses, advection, mixing, suspended particulate matter, chlorophyll, and possibly colored dissolved organic matter. This information is useful in studies of physical, chemical, biological, and geological processes. Satellite observations have even greater value when they are combined with related in situ measurements to validate the interpretation and to extend the observations to variables that can not be detected by satellites. Some of the limitations in relying solely on satellite observations are that subsurface features will not be detected (below the first optical depth for visible or infrared wavelengths). During periods of clear skies AVHRR and ocean color imagery can provide information on changes in surface properties over time, but cloudiness creates gaps in such remote sensing time-series and we are often not able to obtain information of surface waters during storms. In situ sensors can overcome these limitations by providing measurements at various depths in the water column and continuously over time. Studies of coastal processes in Hong Kong waters have used both satellite remote sensing and in situ sensors. We developed a Marine Environmental Mapping System (MEMS) that provides high spatial resolution measurements in surface waters of temperature, salinity, dissolved oxygen, pH, and chlorophyll fluorescence from a small boat while underway. These sensor systems were used to obtain high resolution time-series at a fixed location off the HKUST campus. The results from MEMS and the time-series have revealed the spatial and temporal scales of physical, chemical, and biological properties in Hong Kong waters.