Study On Radiation Characteristics And Satellite Monitoring Of Sea Fog By Remote Sensing Over The Yellow Sea And Bohai Sea

The horizontal visibility at the surface of the ocean decreases to less than 1km,when the sea fog occurs. It takes some difficulty to the ship safety, and some troubleto human production, living and wealth. Due to the measurement station is rare, thetraditional in situ measurement is difficult and unfeasible to observe the fogphenomenon in real-time or in large range. Luckily, satellite measurements providethe way and mean to detect the sea fog in near real-time and in large range.In this paper, fourteen AVHRR/NOAA17 satellite datum, which act as aforehandresearch events, and simulates by radiance transfer model (Streamer) are used to theresearch on radiance properties of sea fog and others. By comparing the differentobject observation and simulate radiance, it shows the major radiance characteristic ofsea fog. On the base of those, a sea fog detection algorithm, which is meaning inphysics, is proposed. And the retrieval of five microphysical parameters of sea fog isdiscussed fully. Using the AVHRR/NOAA17, the detection algorithm is run throughfive months (Jan to May, 2006). By comparing and analyzing, the precision of fogdetection is validated and the limitation is pointed. Lastly, the representativeapplication is successfully done on Chinese polar-orbit meteorology satellite FY-1D.Some significant results are revealed as follows:1. The reflectivity of sea fog at visible and near-infrared channels satisfies:Ch1＞Ch3a＞Ch2, or maybe Ch3a＞Ch1＞ch2. This radiance characteristic is mainlyconducted by the relative size of sea fog and three channels. This result providesimportance scientific argument for the sea fog detection and the judge of small sizecloud particles.2. The difference of mid- and high cloud at the near-infrared channel is that highcloud, Ch2＞＞Ch3a; mid cloud, Ch2＞ch3a. It shows that the reflectivity at channel 3aof NOAA17 is used to judge the cloud phase.3. The reflectivity at Ch1, which varies with the cloud optical thickness, and thereflectivity at Ch3a, which is the function of the size of cloud/fog particles, isapproved. Therefore, combining the reflectivity of Ch1 and Ch3a, the retrieval ofmicrophysical parameters of sea fog is possible and feasible. 4. Based on those radiance properties, an algorithm, which is used for sea fogdetection over the Yellow Sea and Bohai, is proposed. The algorithm is meaning inphysics by six steps: (1) separating of cloud and clear region; (2)judging the cloud phase; (3) differentiating of the size of particle; (4)analyzing the picture characteristic;(5)distinguishing the cloud height; and (6)repairing the lost pixels. By analyzing thedetections of the 14 aforehand events and five months continuous satellites, it showsthe algorithm has the ability of sea fog detection in large range and near-real time.The application tests for FY-1D satellites is successful. The wide applicability of thealgorithm is presented5. The relationship between the efficient radius, the fog optical thickness,visibility, fog water content is analyzed and deduced. Assuming the fog sizedistribution, the relation between the number of fog drop in unit volume and visibility,fog water content is created. Then, on the base of fog detection, linking the satellitereflection of Ch1 and Ch3a, the five fog microphysical parameters is derived by LUT.6. The detection of sea fog over the Yellow Sea and Bohai for a long time isanalyzed. The fog detection is weak for: (1) the ocean region affected by Asia dust; (2)the fog region sheltered by high cloud; (3) the edge of some low cloud. It gives thedirection of improving on fog detection in the future.Some innovations is listed as follow:1. After analyzing the radiance characteristic of the different object by satellitemeasurements and model simulations, the reflectivity of sea fog at visible andnear-infrared channels satisfies: Ch1＞Ch3a＞Ch2, or maybe Ch3a＞Ch1＞ch2 is found.Those provides the important science base for the detection of sea fog and the judgeof small size cloud particles.2. Based on those radiance properties, an algorithm, which is meaning in physicsand wide-application for others, is proposed to detect sea fog events over the YellowSea and Bohai. After applying for satellite measurements in a long time, it shows thatthe algorithm has the capability for detecting sea fog event. And it have get successfulapplication test for FY-1D.3. The fog microphysical parameter is first studied exploringly in home. Itgives important technology for filling up microphysical parameter which is difficultto measure over ocean.