Remote Sensing Application


Facilities
An HRPT (High Resolution Picture Transmission) station for the reception of SeaWiFS (Sea-viewing Wide Field-of-view Sensor) ocean color data was installed at the Hong Kong University of Science & Technology (HKUST) in 1994. Since then, we have been receiving transmissions from NOAA (National Oceanic and Atmospheric Administration)-12, -14 satellites and the SeaStar satellite which contains the SeaWiFS instrument. 
Coverage
All NOAA and SeaStar satellites operate in near-polar sun-synchronous orbits at heights of about 850 km and 750 km respectively, and provide global coverage twice a day. The sensors on the satellites scan the earth continuously and broadcast data at the same time.AVHRR (Advanced Very High Resolution Radiometer) is available on all NOAA platforms. It has a 1.1 km field of view at nadir and is a five-channel device transmitting in the visible, near-infrared and infrared wavelengths. 
Data Processing

Monthly averaged SST over theSouth China Sea for 1995

Features during different seasons in HK's coastal waters and the Pearl river estuary
Sea Surface Temperature
NOAA/AVHRR infrared channels 3, 4 and 5 are used to calculate Sea Surface Temperature (SST) using the MCSST (MultiChannel Sea Surface Temperature) algorithm. The temperature is in degrees Celsius.
Suspended Matters in Water
AVHRR channels 1 and 2 are used for the study of the distribution of suspended matters. An Atmospheric correction algorithm is applied to Channels 1 and 2 so that we may get a quick yet useful look at the suspended matter in the waters near Hong Kong.
This image shows the distribution of suspended matters in the Yellow Sea and East China Sea. The large area of turbid water mass (yellow and brown) is located at the ancient Yellow River estuary.
Applications
 
Indonesian Fire
  Tropical Cyclone
  Red Tide Observation
  Air Pollution in Hong Kong 



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Indonesian Fire
   

AVHRR data were used to track and analyze the 1997 Indonesian fires and the dispersion of smoke. Although Indonesia is at the southern extremity of our reception area, high quality pictures though with partialview were received.

 

 

 

These images combine the visible, near-infrared and infrared channels. Smoke appears in yellow or yellow-white color over the land and water, clouds appear in a white or white-blue color, land appears in a green color and water appears in blue color. The red dots are the fire points.

 

 

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Tropical Cyclone
 
This is an image of typhoon Helen, one of the tropical storms affecting HongKong in 1995. AVHRR visible and near-infrared channel data are used to create this picture. 

The infrared image shows another typhoon at nighttime. 

Tropical cyclones with maximal sustained winds of greater than 118 km per hour (33 m/s or 64 knots) are called typhoons. Using visible and infrared images from AVHRR, cloud patterns and overall structures can help us determine the location and intensity of tropical cyclones and typhoons.

 

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Red Tide Observation
Images showing the changes in chlorophyll concentration during the period of red tide.

Images showing the changes in sea surface temperature during the period of red tide.

China has been experiencing increasing red tides off the Chinese coast since the 1990s due to increasing pollution caused by industrial waste water. During the past decade, a total of 200 red tides have been registered and over the past three years there have been 45 major red tides, causing 240 million U.S. dollars in direct economic losses. With the help of remote sensing technology, we can monitor red tides based on the satellite images of chlorophyll concentrations and sea surface temperatures in water.

 

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Air Pollution in Hong Kong

Ching Ming Festival
Numerous wild fires broke out during Ching Ming Festival  1999 in HK as well as in the coastal region of Guangdong  Province. During the period of April 6-8 1999, very high API were recorded around HK. Using remote sensing technology and NWP system results, hot spots in the region were located.

 

Tung Chung
The API for the western part of Hong Kong increased to a very high level several days before the end of 1999. On 30/12/1999, the API at Tung Chung topped 161, an all-time record high since measurements have been taken. With the combination of remote sensing techniques and NWP system results, we were able to locate the pollution source in the Chinese mainland and show the movement and dissipation of the smoke and haze.