1.What is MDD
Processed satellite cloud imageries ,
analyzed fax charts and coded weather messages were disseminated through INSAT
Meteorological Data Dissemination (MDD) scheme since 1989. The transmission of
cloud imagery data was done in analogue
form and therefore the images had
limited operational use and not
usable for detailed quantitative analysis in weather forecasting. Also the
transmission of cloud imageries took about 10 minutes for one image. The
quality of satellite imagery received
from this system was sometimes
adversely affected due to noise and transmission problem inherent with analogue
based systems.
The limitations of the old MDD system
were : -
i)Analogue system was more prone to noise .
ii)More time required for image
transmission .
iii)Data was not useful for quantitative work .
iv)Technology was old and needed replacement .
v)Spares were not available .
vi)Useful life of the equipment , 8-10 years , which had been expired .
2. What is DMDD
Since the analog technology was old and the
systems had outlived their useful life, it was decided by the competent
authority to replace the old MDD
receiving systems with the latest state of art system - The Digital MDD
System(DMDD) . Digital Meteorological Data Dissemination system is a technique
of transmitting meteorological data (viz. Cloud pictures, GTS data and Analyzed
Weather Charts) through Satellite (at present INSAT-3C) in digital form using
LRIT/HRIT format. At present 37 numbers of DMDD systems have been installed at
IMD field stations through out the country (Regional Meteorological Centers,
Meteorological Centers, Aerodrome Meteorological Offices, Flood Meteorological
Offices, and Cyclone Warning Center etc.) to receive data through INSAT-3c.
This system has many advantages over the conventional technique, like low
noise, very short of transmission and reception time, advance technology, more
storage, data analyzing/plotting capacity etc.
The
DMDD data up-linking to satellite is also done by Indian Meteorological
Department (IMD) from Satellite Meteorological Division, IMD Lodi Road, New
Delhi. This has increased the reliability of transmission. Besides IMD, the
data transmitted is also received and used by IAF/NAVY/SASE. This system has
ben installed at three neighboring countries viz. Nepal Maldives and Sri Lanka.
3.Advantage of DMDD
It was also observed that very often the MTNL link
between IMD and Delhi Earth Station, Sikindrabad failed and the field stations
did not get the required cloud pictures and other data in time which was very
useful for their weather forecasting .
Because of these problems it was
also decided to have own satellite
up-link system along with the down-link system .
The Digital MDD system has many
advantages over the analog system .
Advantages
of Digital MDD system :-
i)
Digital transmission – consumes less satellite power and noise is also
less .
ii)
Transmission of satellite image
takes less time depending upon
the
type of the picture i.e. volume of
data .
iii)
Data transmission rate 64/128 Kbps and modulation type - BPSK/QPSK .
Analysed Fax
weather Charts and conventional Met data are also being transmitted
in Digital format i.e.*.jpg and
ASCII files .
The
proposal to switch over from
analogue MDD to Digital MDD was in order to further improve the quality of
operational data received at the field stations, to shorten the time of
transmission and to improve utilization of data by field offices consuming less
power of satellite . It is proposed to replace
all the old MDD receiving equipments which were installed in two phases
. It was also proposed to install
uplink facility equipments at IMD
campus for Digital MDD and other associated equipments needed for the
implementation of the scheme. Technical feasibility of this scheme was
already established in an experiment
conducted jointly by IMD and SAC scientists in Delhi in December, 2000. The
technology for this system is therefore available in India.
The MDD equipments installed at 35
locations were of old technology. 25 stations were installed during 1989 to
1995 and 8 stations during 1997- 1999.
These old equipments needed replacement for efficient dissemination of frequently available satellite imageries and
weather products for operational use by the weathermen all over Indian
continent and two stations in
neighbouring countries at Maldives and Sri Lanka . It was decided that the
replacements of old MDD system will be done in two phases on operational
priority basis . The new technology will also improve quality of data and give
rise to improved utilization of data at field stations.
The availability of improved quality of
INSAT Satellite imageries, analyzed FAX charts and meteorological data at
forecasting offices on an operational
basis in real time will enhance the
weather forecasting capability of the Department. Uninterrupted data
availability at field stations located all over the country and in neighbouring
countries will help in better monitoring of weather systems on an operational
basis which will give rise to improved forecasting services to the users.
Particularly in the cyclone prone coastal areas of India, availability of such
data will give rise to better monitoring of cyclonic storms. Field forecasting
officers can also use improved quality of MDD data for research work on various
operational aspects of weather forecasting.
4.Featurees and facilities in DMDD
sysytem
It was decided
that the DMDD will gradually replace all Analogue MDD stations in the country
in a phased manner. Initially about 40 stations of IMD are proposed to be
replaced with DMDD receivers and
workstations along with one DMDD uplinking equipments (in redundant mode) at
IMD HQ. New Delhi.
LRIT / HRIT formats has been introduced for
dissemination of Satellite imagery, Satellite data products, Weather Fax charts
and conventional meteorological GTS data
as per WMO and CGMS guidelines for users in Global formats .
Technology development
SAC has
developed technology for a similar
system called Digital Sound and Data Broadcast (DSDB) system for use in INSAT
system. This system is being currently manufactured by Indian industry. IMD has
also implemented recently a similar scheme in A.P. for Digital Cyclone Warning
Dissemination System as part of the
World Bank Project of Govt. of Andhra Pradesh. Technology for proposed new DMDD
system is similar to this system.
Uplinking station
Digital data containing cloud imageries, WMO coded
weather bulletins / messages (GTS data) and fax charts are available at IMD, New Delhi in standard
formats for up-linking to INSAT satellite in C- band using one of the allotted
Radio Networking (RN) carrier frequency from IMD, New Delhi. These data are
converted into LRIT / HRIT formats
before up-linking to INSAT as per
WMO and CGMS specifications CGMS–XXUI-FUM-WP-28 dated 12th may 1998. Redundant Hardware and Software for pickup,
reception, storage, conversion of data files into LRIT/HRIT formats, encryption
of data files for LRIT / HRIT formats and to facilitate transmission in a
predetermined manner/ schedule are being
supplied. Other required equipments such as up-linking equipments, monitoring
and control (M & C ) system for each and every device through software and
automatic switching software in case of failure of online device (s) for uninterrupted service,
without operator intervention, in a fully redundant configuration are the part
of the supplied system. Display of status of system through an ONLINE / STANDBY
block schematic on the screen also forms part
of the system. System manager,
supervisor, operator privileges and tools
provided for specific functions like device control, maintenance,
debugging, switch over, status monitoring, modification of operation schedule,
preferences etc. through the M & C
at the up-linking station .
The
transmit system located at IMD CAMPUS,
NEW DELHI consists of -
Out
door units :
•
Antenna
•
RFT
with redundancy switch
•
Indoor
units :
•
Data
reception PC Workstation
•
Data
conversion from original data formats to LRIT/HRIT formats, other encryption,
decryption, tools to be given as option.
•
Data
encryption software tools
•
Software for data transmission
•
Diagnostics
and maintenance tools, log files, statistics, histograms, plots, graphs,
archival, restoration, system and data backup tools, online manuals and help
etc.
•
BPSK/QPSK
Modulator
•
RFT
control switch
•
DMDD
monitoring and Control System.
•
Redundancy
switches .
C-band antenna system is a 3.8 m offset-fed antenna, which
has been installed near the existing IMD Earth Station . Transmit equipment fully redundant chain
(1+1) with automatic switch over in case of failure including redundant P.Cs
for LRIT/HRIT conversion. Antenna supplied is not redundant.
Digital
MDD Overview
:-
Digital data containing cloud imageries, WMO Coded Weather
Bulletins/Messages (GTS data) and fax charts are available at IMD , New Delhi
in standard formats.
These data are converted to LRIT/HRIT formats and packets of
data are fed through the LAN port to
Uplink Earth Station.
Packetized data received from LAN port at high speed are converted to Continuous data at lower
speed. The above processed data has to be Up linked in C Band to INSAT
satellite by an Earth Station located at New Delhi. The data rate is 64/128
Kbps. The data has to be received at Remote Stations in S Band (at present 40
Nos.) located all over India.
DMDD Uplink System :-
Data rate for Up linking 128 Kbps. (at present)
Up linking is done in C Band.(frequency 5886 MHz)
Redundant H/W is used
for Up link system (except Antenna)
Automatic Switching from On-Line to stand-by in case of
failure of On Line H/W without operator intervention. Monitoring and control is
also provided for Up link H/W.
RF Link via Satellite from Base Station to Remote
Station available, Reverse Link not available. Down link is done in S
Band(frequency 2586 MHz). Down link is received by
1.2/1.8m.Antenna. UPS is also provided for Remote Station
for back up more than 2 hours.
6.BLOCK
DIAGRAM OF DMDD (Tx) SYSTEMS
The transmission system consists of : -
(i)
Workstation which receives cloud pictures
from IMDPS, GTS data and analysed weather charts from Telecom Division. These
data is converted into LRIT format and transferred to the transmitting system
in packets.
(i)
RAD Unit receives data from workstation
and feeds it to modulator
(ii)
The Modulator modulates (QPSK modulation) signal and feeds it to Up-converter .
(iii)
Up-converter up converts the modulated
signal to the desired signal of frequency 5886 MHz
for transmission to Satellite .
(iv)
HPA( High Power Amplifier) amplifies the
signal received from Up converter to the
desired level ( at present 40 W ). The out put of HPA is fed to LNA through
wave guide and finally is transmitted to the satellite through antenna.
(v)
Antenna- a 3.8M parabolic, offset solid dish antenna directed
to wards INSAT-3C .
The
whole system is on hot redundancy. In case of any reason if one module of the
main channel fails, the standby unit takes over automatically.
Data interfacing :-
Data is to be received from PC LAN port .
This data is in the form of standard Ethernet packets at the bit rate of 10
Mbps.
Interface Converter Ethernet Bridge (RAD Make ) for converting
LAN Data to sync. RS 422 data is used. Present data rate to be used 128 Kbps
(Modem will decide the data rate).
Ethernet Bridge provides compatibility
between the PC interface (Ethernet /LAN standard) and the Modem standard Sync
data with clock.
Modem :-
To process data for providing forward error
correction and QPSK modulation .The module has both modulation and demodulation
functions, only modulation is being used . The Output of Modem (modulator part)
will be modulated 70 MHz. The data rate
of 128 Kbps is set in modem. Data rate 64/128 Kbps and modulation type
BPSK/QPSK both can be used . Modem will provide reference clock (Tx clock) to
Ethernet Bridge (RAD).
Up Converter :-
It Receives 70 Mhz signal from Modem. It up converts 70 MHz to C Band frequency ( 5886 MHz .) .
Output of Up converter is fed to HPA .The input signal of 70MHz is converted to
C band in two stages , in the first stage it is converted to L band . A fixed
frequency IF LO performs this conversion . The Broadband Synthesizer provides
the synthesized Local Oscillator for conversion from L band to RF output .
Filters are used at the output of both first stage and second stage to remove
the undesired frequencies which are obtained at the output of Mixers .
HPA ( CLPA - Compact Low Power Amplifier ) :-
The HPA provides amplification to the low level in
put RF signal in C Band received from up converter. It has maximum
capacity to provide 200 watts output .The unit has Traveling Wave Tube ( TWT )
, Solid State Intermediate Power Amplifier
( SSIPA ) , Input Output Isolation circuits . Input attenuation , RF
detectors and output filter . The combined gain of SSIPA and TWT is 75 dB. TWT
is designed for compact light weight
application involving Satellite Uplink service. Output of
TWT is interfaced to wave guide assembly consisting of isolator , Harmonic
filter , Receive rejection , Filter and 3 port directional coupler .
Antenna :-
3.8 m Antenna is used to receive RF signal from HPA via C
band wave guide and transmit the signal
to the satellite. Antenna aligned to face toward INSAT 3C Satellite. It
is a parabolic off set antenna with solid Aluminium reflector . The antenna can
be controlled by the Antenna controllers mounted in the Equipment room . The
antenna is manually controlled . The parameters such as Az/El angles, polarization
can be changed with the help of Antenna Control Unit.
DMDD
Receiving station
The data uplinked from New Delhi in
C-Band , frequency 5886 MHZ.are being broadcasted in S-Band, frequency 2586Mhz
at data rate 64 / 128 Kbps for reception all over India & in the
neighboring countries as per the foot prints of the INSAT-3C satellite. The receiving system consists of an antenna of about 120 cm
diameter . LNBC, L-Band DSDB Receiver,
UPS, Batteries and a latest state of art data reception & processing PC
workstation along with i9” Colour Monitor, 2 X 80 G.B. HDD, 1.44MB FDD,
Keyboard, Mouse, CDR/W, CDROM, Graphic support, one colour Laser Printer
(1200x1200 dpi) or better and one Inkjet/DeskJet (Colour & B/W) printer and
necessary Software for reception, decryption, reconversion of LRIT / HRIT data files / data into
useable formats for day to day
forecasting applications. The workstations have image animation, contouring
and all the required software support for viewing, Editing, printing, plotting,
view Graphs and manipulation of data utilization for the weather applications.
Data overlay for temperature contours & imagery etc. support are available.
Enough Hard disk space to store one month imagery & data files along with
archival, restore & backup facilities on DAT cartridges for day to day use
and necessary Software & Hardware tools, diagnostics have been provided.
Basic features of the
Remote Stations:
ABOUT DMDD SYSTEM
In DMDD (Digital Meteorological Data
Dissemination ) system, the up-linking of data signal to INSAT-3C is done by
IMD from IMD campus at Lodi Road, New Delhi-110003
Block
Di-gram of DMDD receiving system
The
transmitted signal is received at INSAT – 3C and retransmitted back at 2586
MHz. which is being received at 40 nos. of receiving stations at different
places.
The receive chain consists of : -
(i)
1.8 meter parabolic, solid , off-set dish
antenna.
(ii)
LNBC (Low Noise Block Converter).
(iii)
RF cable ( 60 meter).
(iv)
Demodulator.
(v)
RAD unit.
(vi)
Workstation- One complete set (PC, 19” colour TFT monitor, Optical mouse
and key board).
(vii) Colour
Laser Printer.
(viii) 2KVA
UPS.
The following types of data
are being transmitted through DMDD System on
regular basis and are available at the ground
receiving system .
(I)
Cloud pictures in two different formats
:-
(a)
JPEG format : - Full globes and Sectors ( which includes Sri Lanka also ) of Visible , Infrared ,
Water Vapour and Colour are transmitted every half hourly .
(b) Binary format : – Full globe
pictures (Visible during day time;
Infrared and Water Vapour during day and night time) . These
pictures are transmitted every three hourly at
Synoptic hours .
These pictures can be used for further
analysis ( like zooming ,
cropping , drawing pressure and temperature
contours both at
surface level as well as at upper levels ,
route forecast etc.) .
(I)
GTS Data
: - Round the clock GTS data are transmitted through
DMDD System in total 48 files
( 2 files hourly ) . In receiving
system these data are stored in separate
files viz. Synop data ,
Upper air data , Rarep data etc.
The Synop data and Upper air
data can be automatically
plotted and also pressure and
temperature contours can be
drawn at user’s choice intervals .
(III) Analysed Weather Charts : - The analysed Weather Charts are
transmitted twice daily ( between 4 to 5 GMT and between
10 to 11 GMT ) .
The system has the
capability of storing data in itself for about one
Month. The data can also
be archived in tapes and can be retrieved when required.
Advantages:-
(i)
Noise is less in DMDD Transmission and
reception.
(ii)
The receiving system are small, compact
and economic.
(iii)
The latest state of art technology has
been used.
(iv)
The system has more capability of data
handling.
(v)
Downlink System
Antenna :-
1.2m/1.8m parabolic off set
antenna with solid aluminium reflector is used
to receive S band signal 2586 ( MHZ ) from satellite .
LNBC :-
To amplify S band( 2586 Mhz )
signal received signal from feed by 60 db, to provide output in L band
(1064 MHz). Input impedance 50 Ohms
Output impedance 75 Ohms .
DEMOD ( SBR 8192
) :-
Demod is used to demodulate
the L Band signal ( 1064 MHz ) , Range 950MHz to 2150 MHz in 1KHz step. (to
recover digital signal from RF ).It accommodates both QPSK/BPSK modulation It provides error correction , the receiver
can operate with either 1/2 , 3/4 , and 7/8
rate K=7 DVB Viterbi error correction and give data and clock in RS 422.
Demod chassis has built in power supply for the demod card. It also provides
18V power for LNBC.
UPS :-
UPS provides uninterrupted
230V ac for the demodulator with battery backup for more than 2hrs.
DIGITAL METEOROLOGICAL DATA DISSEMINATION
WORK STATION
metGIS Digital Rx :
This is a state of art image processing system . The system
receives cloud imagery data from various sources like HDF4, HDF5, JPEG and GIFF
supplied by IMD and displays it on a high resolution color monitor .The image
thus displayed can be further enhanced using different image processing
functions like contrast stretching ,
inverted etc. and focus can be taken to relevant portion of the image .
the data received can be plotted by values or contours on a specific image .
The system will receive WMO and Weather bulletin in messages either in ASCII or
in BUFR format and fax chart in standard JPEG format. metGIS Digital Receive
system provides an important tool to the
meteorologists who can make analysis based on the data received through various channels and
interpret the same with the satellite images received .
This software provide facility of Geo-referencing
satellite images automatically provided these are transmitted and received in
standard format . These are global
satellite images received through DMDD in LRIT format . All Weather
messages/GTS data and Satellite Images will be received in the form of LRIT (
Low Rate Information Transmission ) files. The system has the facilities for
defining image processing and analysis
sequence with typical macros, zooming , animation , cursor movements ,
density slicing etc. The most important feature of metGIS Digital Rx is
navigation /geo-referencing of full globe satellite images.
These enhanced images can then be stored on a permanent
storage device of the system in the well designated robust database for later use
. The images can be printed in either monochrome or colour .
System
Overview : -
•
Digital Meteorological Data
Dissemination (DMDD) system will transmit and receive the following types of
data digitally in the form of LRIT/HRIT , as per CGMS standard:
•
Cloud imageries .
•
WMO coded weather bulletins/messages
(GTS) .
•
Fax charts .
•
Above pre processed data will available
at IMD, New Delhi from various sources and further processed to LRIT format for
transmission using metGIS Digital Tx software .
•
Further after reception, images and
data can be visualize, analyzed using metGIS Digital Rx software .
Transmission System Overview
Reception
System Overview
System Features:
•
Latest technology hardware.
•
Redundant systems for high reliability.
•
Automatic Reception of input data
pushed by IMD servers via FTP.
•
Automatic/Manual mode for transmission
.
•
Creation of LRIT as per CGMS standard.
•
Digital Transmission .
•
24 hour data backup .
•
Automated data deletion .
•
Automated file reception .
•
Automatic data base updatetation .
•
Image analysis .
•
Image processing features.
•
Printout of required Images
•
Animation .
Introduction of LRIT/HRIT :
The
intention of LRIT/HRIT is to define a standard for dissemination of data,
preferably from geostationary spacecraft towards LRIT/HRIT user stations. The
main approach of LRIT/HRIT is to disseminate standardised image data mapped to
the surface of the earth, preferably those generated by or deducted from
satellite remote sensing data. Additionally, LRIT/HRIT shall provide means to
forward other types of graphical information, alphanumeric data or binary data.
The (digital) LRIT mission shall replace the (analogue)
mission.
LRIT is intended for use on low rate
communication links, mainly at 10 kbit/s until 256 kbit/s. HRIT is intended for
use on high rate communication links, mainly at 0.256 Mbit/s through 10 Mbit/s.
MetGIS Digital Tx
Software Features : -
•
Developed in JAVA, Hence Platform
independent*. However the software is configured on Linux OS as per requirement
of India Meteorological Department.
•
Automatic Reception of Satellite
images, GTS, Fax Charts from IMD servers pushed via FTP.
•
Automatic extraction of usable data
from different formats.
•
Automatic preview of the received
images or data from IMD servers.
•
Automatic creation of LRIT files as per
universal CGMS standard for digital transmission.
•
Automatic LRIT processing.
•
Dual operations (Live/Standby) of data
for better reliability using LINUX HA.
•
Transmitting Warning or Priority
Messages along with the outgoing Transmission
•
Capable to Transmit Compressed as well
as Encrypted data (For security).
•
No operator intervention required.
•
Transmitting data manually according to
user specification. (Can transmit fresh images or already converted LRIT
files).
•
Password Settings for security purpose
of the Software
•
Display of data Back-up transmitted in
Last 24 hours.
•
Tracking of each event in form of Log
Viewer.
•
Option of transmitting various types of
images.
•
Error messages and suitable help menu.
MetGIS Digital Tx
Software Modules :
•
RECEIVING FTP DATA
•
LRIT CREATION
•
LOG GENERATION
•
SEGMENTATION
•
PACKETISATION
•
DATA TRANSMISSION THROUGH UDP (AUTO
& MANUAL MODE)
•
EVENT VIEWER
Operation &
Maintenance of Equipmements :-
•
Configuration & Settings
•
Packets Reception
•
Error Detection
•
Packets Validation
•
De-Packetization
•
LRIT Decoding
•
System Maintenance
•
System Recovery
Ground Receiving Equipments:
System Modules Description
•
Reception (Image, GTS, Others)
•
De Packetization
•
LRIT Decoding
•
Log files
•
Data Storage Tools
metGIS Digital Rx.
Software Feature :-
- Satellite
tranamission is Digital.
- Developed
in JAVA, hence platform independent. The software is configured and ported
on Linux OS as per requirement of IMD.
- More
accuracy and reliability as compared to analogue reception.
- All
Weather messages/ GTS data and Satellite Images will be received in the
form of LRIT ( Low Rate Information Transmission ) files.
•
Setting of Resolution of Monitor.
•
Print Image with or without Analysis.
•
Display of image on full screen.
•
Enhanced Satellite Image Quality
•
Geo-referencing of full globe image on
the base-map.
•
Sectorization of geo-referenced full
globe images, on the basis of latitude- longitude and line pixels.
•
Temperature contouring.
•
Wind Vector contouring
•
Enhanced Animation features.
•
Event viewer (log files) for data
reception.
•
Raw Data Viewer – raw data stored in
the database can be viewed for user specified date, GMT and station name.
•
BUFR ( Binary Universal Form for
Representation of Meteorological Data ) Data decoder has been incorporated to
metGIS Digital Rx.
•
Capable to plot the RAREP, SYNOP, UPPER
AIR data on specific imagery/base map as per requirement of India
Meteorological Department.
•
Window Splitting for comparison of
images.
•
Capable of geo-referencing
(automatically/user-interactively) for images being received through DMDD.
•
Image processing functions like density
slicing, color balance, contrast stretching etc.
•
Facility for generation of Contours on
satellite image as well as base map.
•
Storage of actual as well processed
images in the database.
•
Printing of actual as well processed
images.
•
Facilities to generate Met Symbols
(WMO).
•
Animation facilities with different
options like selection of stack, frame speed, reverse animation, storing of
animation etc.
•
Facility to write messages on satellite
images.
•
Error messages and suitable help menu.
INSAT 3C S BAND
The diagram showing EIRP of INSAT-3C down link.
EIRP (Effective Isotropic Radiated Power) – is the
apparent power transmitted towards the receiver, if it is assumed that the
signal is radiated equally in all direction, such as a spherical wave emanating
from a point source
INTRODUCTION :-
India
is a large country with coastline of about 8000 kms. which makes the country
vulnerable to severe Tropical Cyclones arising in the Bay of Bengal and Arabian
Sea during Pre-Monsoon
( April
and May ) and Post-Monsoon ( October to
December ) seasons every year . The
tropical cyclones are most destructive weather systems and are mostly associated with torrential rain , very
strong wind and storm surges causing
huge loss of human lives , cattle ,
crops and other properties . Cyclones can not be prevented but the losses can be considerably reduced if
warnings are issued well in advance to the areas likely to be affected by the
approaching cyclones so that the local administration can take adequate measures .
With this theme
India Meteorological Department.( IMD ) started cyclone warring services to the
country and monitoring the movement of
the cyclones from the day one of the
cyclogenesis and issuing warning to the public and the Govt. officials for taking mitigation
measures to evacuate the people likely to be affected to the safer places to
save them from the heavy rainfall , strong winds and tidal waves associated with the cyclone
via TV , Radio , Telephones , Telegrams , Tele-printers and other media . With
the advancement of technology and launch of INSAT ( Indian National Satellite )
a new thrust has been given to the cyclone warning services to the country
.
Cyclone Warning Centres in IMD :-
India Meteorological Department. has
established three Area Cyclone Warning Centres ( ACWCs ) at Kolkata , Chennai and Mumbai and
three Cyclone Warning Centres(CWCs) at Ahmedabad , Bhubneswar and
Vishakhapatnam for providing cyclone warning services to the maritime states .
Warnings against the adverse weather due to cyclone are issued by these centres
for their respective areas of responsibility to various users like port
authorities , commercial shipping,
Indian Navy , fishermen and
officials of Department of Fisheries , officials of the State and Central Govt.
, Relief officials , Chief Secretaries of the coastal states , District
Collectors , Tehshildars and BDOs for
distress mitigation as soon as the warnings are received by
them . The warning are issued to these officials in two
stages. In first stage a
“ Cyclone
Alert ” is issued about 48 hrs. in advance
of the commencement of the adverse weather over these areas . In second
stage the “ Cyclone Warning ” is issued about 24 hours in advance .
Warning Dissemination
:-
IMD
constantly examines the Arabian Sea and Bay of Bengal areas for likely genesis
of tropical cyclones with the help of satellite imageries received through INSAT
( a
Geostationary Satellite ) . Information
from ships and ocean buoys
is also considered . There is
a chain of Cyclone Detection Radars
( CDRs )
installed along the coastal belt of India . These Radars can locate and
track the approaching cyclones within
the range of 400 kms. Information about the cyclone , such as
areas likely to be affected , its intensity , direction of movement ,
time of reaching the coast etc. are prepared at the Area Cyclone Warning
Centres (ACWCs ) . based on these , warning messages are issued at regular intervals from ACWCs
(at Chennai, Kolkata and Mumbai) through different modes mentioned above . These modes of communications mainly depend
on land line which are not very reliable and are likely to be disrupted during
adverse weather condition particularly during cyclones .Satellite signals are
available to anybody , anywhere , all the time and are not affected by the
adverse weather conditions .
To over come above problem a
satellite based system for dissemination of cyclone warning was started by IMD
in consultation with Department of Space using broadcast capabilities of INSAT
satellite in the C / S Band transponder in 1985 . This system is named as CWDS
( Cyclone Warning Dissemination System )
and as its technology is analogue based , it is called ACWDS and is still operational since last 25 years.
Technical Description of ACWDS :-
The Disaster
Warning System is an important application supported by INSAT and is used for
dissemination of cyclone warning messages to the likely affected areas . The
INSAT supports transmission of a narrow band low level carrier for disaster
warning system along with four RN ( Radio Network ) Channels and TV channels
with S-band . The code transmitter is located at ACWCs . The identification
code of receivers , to whom the warning is addressed , is transmitted from the
ACWCs on DOT ( Department of Telecommunication ) lines to the earth station .
the voice messages are also transmitted using separate DOT lines . At the earth
station , these signals modulate a designated IF carrier of 54.225 MHz. The
modulated IF carrier
is multiplexed with
other IF carriers , Up - converted , Amplified and transmitted
in
C-band at
5859.225 MHz.
Transmission
from INSAT satellite down to earth is in the S-band at a carrier frequency of
2559.225 MHz. At the receiving stations this signal is received by a 3.6 M
parabolic mesh type dish antenna . The
Front End Converter ( FEC ) , which is
mounted on the feed of the antenna , eliminates the undesired noise , amplifies
the signal and converts the S-band signal to IF signal . The IF signal is
filtered by using a helical type narrow bypass filter to remove the TV signals
. The signal is then amplified and
demodulated using a frequency discriminator . The output signal is fed to the
digital cards for detection of codes and
subsequently activation of the siren and loud speaker .
The DWS works
in broadcast mode and the operation is completed in two stages . The entire
cyclone prone area is divided into various zones . The receivers located in a
particular zone will have the same identification code . When it is required to
address a particular zone , the code corresponding to that zone is set and transmitted . The
receivers pertaining to that zone will detect the code and activate the siren ,
which attracts the attention of the local officials . In the second stage the
voice message follows the siren and the officials can take the necessary action
.
List of
Analogue CWDS Stations installed in India –
1. West
Bengal 31
2. Orissa 35
3. Tamil Nadu 56
4. Pondicherry 03
5. Andra
Pradesh 79
6. Kerala 05
7. Karnataka 05
8. Gujrat and
U.T. 22
9. Maharastra
and Goa 09
10.Monitoring
stations 07
------------------------------------------
Total 252
Digital CWDS
:-
Later , IMD has also
implemented the scheme of Digital CWDS ( DCWDS ) in Andhra Pradesh under Andhra
Pradesh Hazard Mitigation ( APHM ) and Emergency Cyclone Recovery (ECR)
projects funded by World Bank . Under
these projects ,one hundred DCWDS receivers have been installed in AP and one in Kavarattti , Lakshadweep Island in 2002-03 with uplink station at RMC Chennai
.
This system has an
additional advantage of reception of Acknowledgement messages through Mobile
Satellite Service ( MMS ) of INSAT and the quality of voice is very good as
compared with analogue CWDS .
The digital cyclone warning and dissemination
system ( DCWDS ) is also designed to work in broadcast mode . It transmits a
pre-selected digital code corresponding to remote station’s receiver located at
the coastal areas that are likely to be affected . Transmission is done from
the small uplink station at RMC Chennai . All the satellite receivers receive the broadcast and only the selected
group of receivers gets switched on their audio output . Alert siren sound and
warning messages are appended to the receiver address code from ACWC . On
reception of warning , the receiver will generate acknowledgement messages
which are transmitted back to the ACWC Chennai through INSAT MSS fixed
reporting terminal attached to the receivers .
The Network
Management System at ACWC Chennai
is responsible for creation , transmission and monitoring of cyclone warning
messages and archival of those messages to unmanned satellite receivers installed all along the
Indian coastal line . The audio messages
captured by microphone are digitalized using MPEG-2 format to create
message packets in a customized protocol , with unique headers for selected
stations . Header and message packets
jointly form a data-packet so that required receivers are only energized by the transmission while others
are not energized . The Acknowledgement messages sent by the remote stations’
receivers are captured , analyzed and checked periodically . All Acknowledgement messages are logged systematically
.
The frequencies used :-
Uplink – 5885.0 MHz , 200 KHz
Bandwidth.
Down link – 2585.0 MHz, , 200
KHz Bandwidth.
MSS Acknowledgement –
Tx. – 2677.560 MHZ , 200 KHz
Bandwidth.
Rx - 3677.560 MHz , 200 KHz Bandwidth.
DTH – Based DWDS ( Disaster Warning
Dissemination System )
India Meteorological
Department stared INSAT – based cyclone warning dissemination system services
in 1985 with a net work of 100 Analogue CWDS (Cyclone Warning Dissemination
System) ( ACWDS ) receivers located
along coastal areas of South Andhra Pradesh
and North Tamil Nadu . Another 150 nos. of such receivers were installed
in early 1990s covering coastal areas of Kerala, Karnataka , Maharashtra ,
Gujarat , Goa , West Bengal , Orissa and North Andhra Pradesh . At present IMD has a
total network of 252 Analogue CWDS receivers and 101 nos. of Digital CWDS
receivers ( 100 nos. in A.P. and 1 no. in Kavaratti, Lakshadweep Island ) . The
DCWDS Receivers were installed during the year 2002 – 03 under Andhra
Pradesh Hazard Mitigation (APHM ) and Emergency Cyclone
Recovery
( ECR ) Projects - funded by World Bank .
Analogue CWDS have served for
about 25 years, more than their useful life( of 10 years)
Being obsolete technology ,
maintenance of these ACWDS receiver is a problem . So, IMD has decided to replace them with a suitable
cost effective technology . In 2007
, ISRO ( Indian Space Research
Organisation ) has submitted a proposal regarding development of addressable
DTH – Based Disaster Warning Dissemination System . In this system, a
commercially available Set Top Box (STB) , after suitable modification , has
been used as DWDS receiver. After seeing its demo, which meets IMD ’s
requirement , IMD had shown their interest in the proposal . IMD , ISRO and
Doordarshan together decided to implement the methodology and commissioning of
this DTH-Based DWDS System. It was
decided that in the first phase , five receive terminals and two transmitting
stations ( Head - ends ) will be deployed by ISRO at IMD’s designated locations
for trial runs . IMD will make arrangement for dissemination of
regular warning through this systems and use it to test its features and
reliability particularly in rainy season . ISRO will also commission a
transmitting (Uplink System) ( HUB ) consisting of one VSAT and a server at Doordarshan’s designated location (Delhi) to
bring audio/data from head-ends to DD hub . Doordarshan will transmit the coded
signal to the satellite through its DTH Bouquet .
ISRO and IMD jointly conceived the
configuration and specification of the Digital Cyclone Warning Dissemination
System for issuing disaster warning to cyclone – prone areas along the coastal
areas from a centralized location . ISRO has taken initiatives to economize the receivers by
modifying the commercially available DTH
( Direct To Home ) Set Top Boxes ( STB ) for this purpose . M/s BEL ,
Bangalore , has been entrusted the task of developing these receivers under the
guidance and support of ISRO .These Systems are known as DTH- Based DWDS
Systems .
Five nos. of receiving Systems have been
installed by ISRO and M/s BEL at RMC Kolkata , RMC Chennai , MC Bhubneshwar ,
CDR Machilipatnam and Collectorate Thrivellor .Two nos. of Head ends,
( SIT – Satellite Interactive Terminals ) have been installed at
RMC Chennai and RMC Kolkata
with centralized control at RMC Chennai . Doordarshan has inserted the disaster
warning channel into their DD-Bouquet. The performances of the systems have
been checked and found working satisfactorily .
Since the existing analogue
CWDS have become obsolete and many of the system have stopped working and are
beyond repair / maintenance , IMD has decided to replace all these ACWDS
receivers by the new DTH-Based DWDS
receivers. It has been decided that total 500 nos. of such systems will be
installed all over the country in the disaster prone areas.
The DTH-Based DWDS System can
disseminate the warning messages in real time to multiple receiving locations
spread over large geographical areas . Each receive location has a unique
address and receivers can be addressed individually or group-wise .
DTH – Based DWDS Receivers ( ROT - Receive Only Terminal
) :-
The receive only terminal (
ROT ) is capable of receiving DVB ( Digital Video Broadcasts ) from HUB
( i.e. Transmitter ) . The ROT System consists
of :-
1) 1.2M
off set feed parabolic dish antenna .
2) Low
Noise Block Converter with Feed ( LNBF ) .
3) Digital
Set Top Box ( STB ) ( MPEG-2/DVB ) .
4) Low
Loss Cable ( RF Cable ) – Maximum length
25m .
5) 10Amp
Charger with two nos. of batteries (
12V/65AH ) to supply 24V DC .
The Ku-band signal (14.0 to
14.5 GHz band ) up-linked from the HUB is translated and relayed by the
satellite ( EDUSAT ) . The down link signal gathered by the antenna dish is
guided into the LNBF . The LNBF processes and down converts the signal frequency
to L-Band ( 950 to 1450 MHz . ) , which
passes through the low loss cable to STB . The STB processes the signal to
recover the video and audio signals. These signals are fed to the Television
set.
DTH Based DWDS Configuration during Pilot-Phase
1) Antenna
: – 1.2M Ku-Band antenna with
an offset focal point . In this antenna , the horn is offset at an angle of 22
degree and placed well clear of the main beam so that no blockage occurs . The
offset arrangement avoids the 10% loss caused in the centre fed arrangement .
The function of the antenna is to collect the signal and feed it to the LNBF .
2) Low Noise Block Converter with Feed ( LNBF )
:- Mounted on the antenna . The function
of LNBF is to pick up the weak incoming
microwave signal ( Ku-Band ) via an internal tuned resonant probe , provide low
noise amplification and finally down convert the whole block of frequencies to
the one suitable for the cable transmission (L-Band) . All the components of
the LNBF are hermetically sealed against the ingress of moisture . If the
moisture gets into the unit – corrosion and subsequent failure may result .
3) Set-Top-Box
( STB ) or Digital Satellite Receiver :- The Disaster Warning Set
Top Boxes (DWSTB) are used to decode the
digitally modulated satellite signals to obtain high quality video and
audio signals and digitally encode data
used for warning dissemination acknowledgement . This unit also supplies DC
voltage to LNBF and receives the L-Band signal from LNBF
through the 25m
low loss cable . The necessary down conversion,
demodulation
( QPSK ) , decoding ( MPEG-2 )
takes place in
it before it
delivers analog video
and audio
signals
suitable for the colour TV Set
.The remote terminals are equipped with BEL DW DTH
Set Top Box operates on 230v AC as well
as 24v DC batteries . India
Meteorological Department has started INSAT-based Cyclone Warning Dissemination
system in year of 1985.At present it has
network of 252 no’s of Analogue CWDS
receiver, and 101 numbers of digital CWDS receiver. The Digital CWDS receiver
were installed by IMD during the year 2002-2003 under Govt. of Andhra Pradesh Mitigation project was funded by World Bank.
3.Status
of Analogue CWDS under RMC Chennai &
Andhra Pradesh
List of Analogue CWDS Stations installed RMC Chennai
Installed Working
Not working
1. Tamil Nadu 56 42 14
2. Pondicherry 03 02 01
3. Andhra
Pradesh 79 59 20
4. 4. Kerala 05 05 0
5. Karnataka 05 04 01 6.Mon. Station 07 07 0
------------------------------------------
Total = 155 119 36
RMC
Chennai reported maximum number of
stations U/S either by shifting of site or construction of new building.
The equipments & Antenna etc of the system becomes rusted and therefore
shifting is not possible. Many stations are also reported receiver problems.