Ocean Remote Sensing in China

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					                                                                                       The Thirteenth Workshop of OMISAR

                    China’s HY-1A Ocean Satellite and its Applications

                                                       Jihui YAN
           National Marine Environment Forecasting Center, State Oceanic Administration, Beijing 100081, China

Abstract                                                       band ocean color scanner (COSTS) and a 4-band
     China launched her first ocean satellite HY-1A            CCD imager.
on May 15, 2002. This paper presents a brief
description of HY-1 Ocean Satellite. Applications
                                                               1.1. HY-1A orbit parameters:
of data from HY-1 in some areas are outlined and
some figures of typical application are provided.                  Orbit type: quasi sun-synchronous, near-circular
Future development of ocean satellite in China is                     polar orbit
also discussed.                                                    Height of orbit: 798km
                                                                   Inclination: 98.80
      China is a country with vast coastal areas that              Equator crossing time: 8:45-10:40am
support rich living and non-living resources,                         (descending node)
including highly diversified habitats. Coastal                     Period: 100.8 minutes
environment and resources are of great importance
                                                                   Repeat coverage period: COCTS: 3 days;
to China’s sustainable development, however, they
                                                                      CCD: 7 days
are suffering increased impacts from over-fishing,
irrational agricultural and industrial development,                Attitude control: 3-axis stabilization
discharging of land-based pollutants, offshore oil
                                                                   Record on board: 80 MB
and gas exploitation and shipping. For protecting
and conserving her coastal environment and                         Weight: 367 kg
resources, China has taken a wide range of                         Designed lifetime: 2 years
measures, including the development and launching
of HY-1A ocean satellite. Studies have been
conducted using HY-1A data in dealing with some                1.2. Specifications of the Payload:
issues related to coastal environment and resources,
such as the detection of harmful algal bloom and oil                (1) COCTS – for measuring ocean color
spill that cause severe negative impacts on coastal            parameters (chlorophyll, suspended sediment
resources. Another important application is the use            concentration, dissolved organic matter, pollutants)
of data derived from HY-1A in the study of ocean               and sea surface temperature. Ground resolution at
primary productivity. Extensive efforts have also              nadir is 1000m, pixels/line is 1024 with
been made in the monitoring of the processes in                quantization grade of 10 bits.
some typical coastal areas, including the content                  (2) CCD Imager: mainly for monitor dynamic
and variation of suspended sediments, and the                  variations of coastal zones. Spatial resolution at
distribution of vegetation in key areas like the               nadir is 250m, pixels/line is 2048 with quantization
Yellow River estuary, the Yangtze River estuary                grade of 12 bits.
and the Pearl River estuary, which is of great
significance to integrated coastal resource and
environment management.                                        1.3. Areas of Observation
                                                                   (1) Areas of real time observation: western
1. HY-1A -- China’s First Ocean Satellite                      Pacific, i.e. the Bohai Sea, the Yellow Sea, the
                                                               South China Sea, the Sea of Japan, and the coastal
    China launched her first pilot operational                 zones. In order to have a full coverage of the seas
ocean satellite HY-1A on 15 May 2002. HY is the                around China, two ground stations were built in
abbreviation of “Hai Yang” in Chinese, which                   Beijing and Sanya respectively.
means “Ocean”. HY-1A is equipped with a ten-

China’s HY-1A Ocean Satellite and its Applications

     (2) Areas outside the Western Pacific: these are         The Radiation Calibration and Sea-truth
areas beyond the coverage of the ground stations.       Verification Sub-system is responsible for radiation
When the satellite comes in site of a ground station,   calibration and sea truth verification. Calibration of
both real-time and non real-time data could be          data from HY-1 is conducted in the China
transmitted to the ground.                              Radiation Calibration Center for Satellite Remote
                                                        Sensing, and sea truth verification is conducted in
                                                        the Yellow Sea and the South China Sea by
1.4. The ground application system                      comparing the remote sensing data from HY-1 with
      The ground application system is composed of      the leaving-water radiation accurately measured in-
a receiving and pre-processing sub-system, a data       situ at sea.
processing sub-system, a product archiving and               The Communication Sub-system is designed to
distribution sub-system, a data application             link the data processing sub-system with the HY-1
demonstration sub-system, a radiation calibration       ground receiving stations, Xi’an Remote Control
and sea-truth verification sub-system, a communi-       Center and various agencies of the Aerospace
cation sub-system and an operation control sub-         Administration to facilitate data transfer and
system.                                                 information exchange.
    The Receiving and Pre-processing Sub-system:             The Operation Control Sub-system is to
Real-time data and delayed-mode data are received       maintain a uniformity of timing for the ground
by the two ground stations at Beijing and Sanya,        application system, control and command the
and these data are pre-processed to produce Level 0     operation of the system and statistically analyze the
and Level 1 products.                                   quality status of the system’s operation. When
     The Data Processing Sub-system is                  abnormal or emergency cases occur, it will take
responsible for the development of hardware             timely and effective measures to solve problems to
necessary for the sub-system and the study of           ensure a normal operation of the system.
algorithms for ocean color, water temperature and
atmospheric corrections. It is also tasked to develop
special software for data processing. Furthermore it
makes COCTS Level 2 and Level 3 products of
ocean color, water temperature and atmosphere,
CCD Level 2 products of vegetation index and
suspended sediments, and develops various
thematic products related to ocean color and water
      The Product Archiving and Distribution Sub-
system is designed to archive remote sensing
products of various levels and provide services to
customers via the data bank’s enquiry, retrieval and
file management system.
     The Data Application Demonstration Sub-
system is designed to use products from the product
archiving and distribution sub-system, to conduct
application research and provide practical
algorithms and relevant software for HY-1A Level              Fig. 1 Ground stations and orbits of HY-1A
3 products, and verifies data of sea water
temperature, sea ice, marine primary productivity
and marine pollution by referring to remote sensing
data from other sources. This sub-system consists
of 7 modules, including: integrated environmental
module; sea ice forecasting module; marine fishery
information service module; marine pollution and
environment monitoring module; coastal zone
dynamic monitoring module and ocean primary
productivity assessment module.

                                                                            The Thirteenth Workshop of OMISAR

2. Applications                                        2.2. Oil-spill detection
2.1. Detection of Harmful Algal Bloom                       Both shipping and offshore oil exploitation
                                                       contribute greatly to the development of China’s
     Harmful algal blooms (HABs) or red tides
                                                       economy. But in the meantime, oil spills by ships
refer to the discoloration of surface water (usually
                                                       and offshore platforms can seriously damage
coastal) caused by the overgrowth or high
                                                       marine living resources and the environment.
concentration of microorganisms, some of which
                                                       Timely detection of oil spills is highly important to
can be toxic, can result in mass deaths of marine
                                                       marine ecological resource conservation.
                                                            Timely response to oil spills on water requires
     Statistics indicate that HABs have been
                                                       rapid reconnaissance of the spill site to determine
increasing rapidly along China’s coast since the
                                                       its exact location and extent. This is of great
1970s. In 2003, 119 HABs cases, like the one in Fig.
                                                       importance to the effective deployment of spill
2, were recorded along the coast of China, covering
                                                       countermeasures such as mechanical containment
a total area of 14,550 km2 and causing a direct
                                                       and recovery, dispersant application and in-situ
economic loss of 42.81 million RMB. Harmful algal
blooms present a growing problem for fisheries,
coastal ecosystems, aquaculture and public health in         Satellite remote sensing is playing an
China’s coastal areas.                                 increasingly important role in oil spill response.
                                                       Through the use of satellite remote sensing, spilled
      Products of ocean color and seawater
                                                       oil can be monitored under most conditions. Study
temperature from HY-1A are used to detect the
                                                       of oil spills and analysis of the optical properties of
initiation, development and decay of harmful algal
                                                       spilled oil indicate that there is a great difference
bloom events and assess their impacts on coastal
                                                       between the reflectance of spilled oil and that of the
resources. On the basis of the analysis of the HY-1
                                                       normal water, and difference also exists between
payloads, the characteristics of data from COCTS
                                                       the water temperature in area with oil spill and the
and CCD and the ecological and optical properties
                                                       water temperature of the adjacent area. These
of HABs, the following algorithms are developed
                                                       features can be used in the monitoring of oil spills.
for HY-1A detection of HABs:
                                                            Two methods are employed in the HY-1A
-- Chlorophyll-a                                       application to extract oil spill information from the
 -- Sea surface temperature                            COCTS and CCD Level 2 products. One is to
-- Multi-spectra                                       extract oil spill information, on the basis of the
-- NDVI (Normalized Difference Vegetation Index)       optical properties of different kinds of spilled oils,
-- Comprehensive judgment.                             by using image classification and identification
                                                       techniques, and the other method is to extract oil
                                                       spill information by using SST gradients to
                                                       determine the boundary between the oil spill area
                                                       and the normal sea area.

                                                       2.3. Marine fishery information service
                                                            Marine fishery environment information is
                                                       indispensable to the conservation of marine fishery
                                                       resources and to the effective operation of fishing
                                                            HY-1A satellite can provide data of sea surface
                                                       temperature and chlorophyll a concentration.
                                                       Further analysis of these data can yield information
                                                       about ocean dynamics such as upwelling and water
                                                       masses. Various fishery environment information
                                                       maps (Fig. 3) or charts can be developed to serve
                                                       fishery resource conservation and exploitation by
   Fig. 2 HAB Information (red) from HY-1A in the      using the Level 2 archived products of sea surface
          East China Sea on 3 Sept. 2003               temperature and chlorophyll concentration that

China’s HY-1A Ocean Satellite and its Applications

were derived from HY-1A COCTS data and other            the initial biomass estimate until the next available
products of environment elements from other             satellite image.
     Fishery information products from HY-1A
include: SST, Chl-a concentration, vortex flow,
ocean front, sea state of fish ground.

                                                           Fig. 4 Ocean primary productivity distribution
                                                                 from HY-1A in Autumn 2002

 Fig.3 HY-1A fishery information product of Tuna        2.5. Dynamic monitoring of typical coastal zones
      fish zone in the Atlantic.                              Information about resources in China’s coastal
                                                        areas has been successfully extracted from data
                                                        provided by HY-1A CCD. The information from
2.4. Ocean primary productivity
                                                        HY-1 has great potential in the survey, monitoring
     Ocean primary productivity (OPP) is defined        and management of resources and vegetation in
as the carbon production per unit time and unit area    typical coastal areas of the estuaries of the Yellow
set by the ocean phytoplankton's photosynthesis -       River, Yangtze River and Pearl River.
taking in carbon dioxide in the ocean and making
                                                              The products for the dynamic monitoring of
carbon, with nutrients like nitrogen and phosphorus,
and sunlight. OPP is estimated from chlorophyll-a       coastal zones include: (1) Types of tidal flats in the
concentration of phytoplankton (Fig. 4), sea-surface    tidal zone of the Yellow River delta; (2) Extent of
temperature, photo-synthetically available radiation,   change and evolution of the tidal zone in the Yellow
and ocean bio-optical models.                           River delta; (3) Dynamic change of the coastline of
     The use of satellite ocean-color imagery to        the Yellow River delta; (4) Spatial and temporal
estimate primary-productivity for relatively large      distribution of suspended sediment concentration in
areas of the ocean is therefore an attractive           estuaries (Fig. 5 & 6); (5) Vegetation distribution in
alternative. In this approach, satellite estimates of   estuaries (Fig. 7); (6) Spatial and temporal
near-surface chlorophyll provide an initial estimate    distribution of water color in the Pearl River estuary.
of phytoplankton biomass (in units of carbon or
nitrogen) as input to a mathematical model of
primary productivity. The model may also require
measurements or estimates of other variables
affecting primary productivity, such as water
temperature, sunlight intensity, and nutrient supply.
Model predictions of daily primary productivity are
then used to calculate the potential cumulative
increase in phytoplankton biomass from the time of

                                                                              The Thirteenth Workshop of OMISAR

                                                       sea ice forecasting in China. Since 8 December
                                                       2002, sea ice images have been made accessible to
                                                       the public in the CCTV Marine Environment
                                                       Forecasting Programme, demonstrating the
                                                       successful application of HY-1A data to sea ice
                                                       monitoring and forecasting in China.

Fig.5   Distribution of suspended sediment
        concentration in Yellow River estuary in
        Oct. 2002

                                                       Fig. 7 Vegetation classification in Yangtze River estuary

 Fig. 6 Distribution of suspended sediments in Pearl
        River estuary from HY-1A CCD

2.6. Sea ice forecasting
       Ice appears in the Bohai Sea for 3 months       Fig. 8 HY-1A image of sea ice in the Bohai Sea on 12
during winter, which would impact offshore                     Dec. 2002
production activities. HY-1A is capable of making
ice observation. Data of ice thickness, the outer
edge of the ice, ice density and ice temperature can   2.7. Sea surface temperature forecasting
be retrieved from the data provided by HY-1A. The
                                                              Sea surface temperature products derived
National Marine Environment Forecasting Center
                                                       from HY-1A satellite data have been directly used
has developed a demonstration system of sea ice
                                                       in daily forecasting of sea surface temperature and
forecasting, using HY-1A database in its
                                                       its research, resulting in the improvement of
operational sea ice forecasting activities. HY-1A
data have become important basic data source for

China’s HY-1A Ocean Satellite and its Applications

forecasting accuracy          and     the    shortening   of
forecasting period.
       The SST products derived include: colored
map of SST distribution (daily, weekly and
monthly), daily analysis product of SST with 10km
resolution, 10-day analysis of SST with 10 km
resolution (Fig. 9 & 10) and the monthly analysis
map of SST with 50 km resolution. The covered
area is 110-160OE,0-50ON.

                                                               Fig. 10    Sea surface temperature Contour (1-10 Feb.

                                                                     China’s first ocean color satellite HY-1A has
                                                               been successfully launched and its products have
                                                               found wide application. The successful operation of
                                                               HY-1A satellite is considered a new milestone in
                                                               the history of satellite development in China.
                                                               However, because HY-1A is an experimental
                                                               satellite, there are many restrictions, such as the
                                                               equator-crossing time, the size and weight of the
Fig. 9 HY-1A 10-day average SST temperature
                                                               satellite, the power system, etc. and the efficiency
      (1-10 Feb. 2003)
                                                               of this satellite is not as ideal as expected, and
                                                               consequently, much remains to be improved. In
                                                               order to further promote ocean observation by
Future Development
                                                               satellite. China has planned to continue to augment
     As stated in the 《White Paper on China’s
                                                               its ocean satellite program in the future and launch
Space Activities 》, China is “to build up an earth
                                                               a series of ocean-oriented satellites. They will
observation system for long-term stable operation.
                                                               include HY-2, which will use microwave
The meteorological satellites, resource satellites,
                                                               technology to detect sea surface wind field, sea
ocean satellites and disaster monitoring satellites
                                                               surface height and sea surface temperature and HY-
will develop into an earth observing system for
                                                               3, which will be equipped with multiple sensors
long-term stable operation to conduct stereoscopic
                                                               such as multi-spectra imager, synthetic aperture
observation and dynamic monitoring of the land,
                                                               radar, microwave scatterometer, radiometer and
atmosphere, and oceanic environments of the
                                                               radar altimeter. Furthermore, ground application
country, the peripheral regions and even the whole
                                                               system, in-situ radiation calibration sites at sea and
globe”. China’s ocean satellites will be an
                                                               sea-truth verification sites will be improved.
important component of China’s satellite observing
network and will, together with airplanes, ships,
buoys and ground-based coastal observing stations,             X.W.Jiang, “Development of China’s Ocean
make due contributions to China’s ocean resource                   Satellites”, 2004
conservation, marine environment protection,                   X.W.Jiang and J.Q.Liu, “Images of China HY-1
coastal zone management, marine resource                           Satellite and their Applications”, China Ocean
exploitation and ocean scientific research.                        Press, Beijing, 2003

                                                 The Thirteenth Workshop of OMISAR

State Oceanic Administration, “Report on the
     Applications of China’s Ocean Satellite--
     2003”, (internal report), pp.1-19, 2004
State Oceanic Administration, “Report on the
     Applications of China’s Ocean Satellite--
     2002”, (internal report), pp.1-19, 2003
Information Office, the State Council, “White
     Paper on China’s Space Activities”, 2000.