SOURCEFORGE » RALF » 2014 Reception of weather images

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h1. 1. Brief history about NOAA satellites

The NOAA/POES satellites are monitored by the association _National Oceanic and Atmospheric Administration_. The NOAA was created in October 1970 for U.S. with the main purpose of provide information about the condition of the oceans and the atmosphere. Concretely, POES satellites send weather information to the _National Environmental Satellite, Data and Information Service_ (NESDIS), which processes and distributes it to the _National Weather Service_ (NWS). NWS is in charge of coordinating the possible warnings to the citizens. 

Before the NOAA agency, first meteorological satellite was launched on April 1960 with the purpose of capturing pictures of the Earth from other perspectives. This first mission was realized by NASA. The payload of the satellite, called TIROS 1, was equipped with two slow-scan television cameras, which take pictures of the Earth. During the next years, additional TIROS satellites were launched improving the technology of the instruments. From 1970 onwards, this industry has been managed and governed by NOAA. The organization recollects the data sent  by the satellites thanks to the NOAA's satellite system and all the information is archived and distributed to the users. The space segment of the system is provided by NASA. Concretely, the research laboratory _Goddard Space Flight Center_ (GSFC) built and launched the NOAA satellites with all desired instruments.

NOAA's system operates in two types of satellite systems. Both types are indispensable for a complete global weather network. On the one hand, _Geostationary Operational Environmental Satellite_ (GOES) provides continuous information in short-term of weather forecasting, several storm tracking and meteorology research. These satellites deliver weather information always in the same place of the Earth. On the other hand, the _Polar Operational Environmental Satellite_ (POES) establishes a large-term link for a climate monitoring and weather predictions. 

From the beginning many satellites have been launched, but the current satellites have a higher level of performance on their sensors. Nowadays, the NOAA's environmental satellites contain the following nine sensors:

* *AVHRR/3*  Advanced Very High Resolution Radiometer 

* *HIRS/4* High Resolution Infrared Sounder

* *AMSU-A* Advanced Microwave Sounding Unit - A

* *MHS* Microwave Humidity Sounder

* *SEM-2* Microwave Humidity Sounder 

* *SBUV/2* Solar Backscatter Ultraviolet Radiometer 

* *DCS 2* Data Collection system

* *SAR* Search&Rescue Instrument

* *DDR* Digital Data Recorder

Once the date is received from POES satellites, NESDIS’ Environmental Satellite Processing Center processes these signals into a set of environmental information products that are distributed to the NWS. ~[1]~

The following Figure 1.1 shows a schema with the different organizations and its involvement in the mission. 

!{width: 70%}picture1_noaa_nasa.png(Figure 1.1: Schematic of the different associations)!

p((((((((((((. *Figure 1.1*: Schematic of the different associations

The benefits proportioned by the environmental satellites are to improve the quality of human life and the protection of Earth's environment. The system is able to detect, forecast and monitoring several storms and national disasters. Also, POES satellites contribute to save lives thanks to the S&R instruments, which are carried on the spacecraft.  

h1. 2. Poes satellites

The polar-orbiting satellites provide data with infrared and visible Earth images in large-term. There is an important advantage in the polar satellites because they recollect information and images of any place on the Earth. The main characteristics of the orbit are the following: 

Nowadays, the fifth generation of these satellites are situated in an altitude over 800 km and they have an inclination around 98^o^, depending of each one.  Its orbital periodic is approximately 102 minutes. Therefore, the satellite system is capable of offering 14 polar orbits a day. Each satellite captures different images of a particular place twice a day.

The data received from the POES series supports a broad range of environmental monitoring applications, including for example:

**  Climate research and prediction

**  Atmospheric soundings of humidity and temperature

**  Volcanic eruption monitoring

**  Land, ocean and atmospheric applications

Currently, a new generation was launched in 2011. The system called _Suomi National Polar-orbiting Partnership_ predicts several weather days in advance. It is also used for measurements, as density of vegetation, clouds, ocean colour and surface temperatures.

The payload will be composed of five instruments: 

* ATMS (Advanced Technology Microwave Sounder)

* VIRS

* CrIS (Cross-track Infrared Sounder)

* OMPS  (Ozone Mapping Profiler Suite)

* CERES (Clouds and the Earth's Radiant Energy System)

A new satellite, called _JPSS-1_, will be launched by the JPSS program in early 2017. The system will be composed of five satellites; therefore, it will improve the accuracy and timeliness of weather event forecasts. JPSS will be able to provide advanced atmospheric temperature and pressure profiles. it will be able to improve the imaging capability to analyze national disasters. ~[3]~

h1. 3. Payload

p(. *INSTRUMENTS*

1. ADVANCED VERY HIGH RESOLUTION RADIOMETER (AVHRR/3)

The instrument detects the energy in the visible and IR frequencies of the electromagnetic spectrum from the sun, land, sea or atmosphere. For example, the AVHRR/3 is able to discriminate the images from snow, ice and clouds. The information data is obtained through the six-channel imaging radiometer with approximately 1.1 km of special resolution. The Earth surface is scanned from a nadir angle of ±55.4° and using 1.3 milliradianes of instantaneous field of view (IFOV). ITT A/CD is the manufacturer of this device.

!{width: 50%}AVHRR.png!

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2. HIGH RESOLUTION INFRARED RADIATION SOUNDER (HIRS/4)

HIRS provides atmospheric information by scanning the Earth each 6.4 seconds with an angle of ±49.5°. The instrument measures in the IR frequencies by mean of a set of channels: one visible channel around 0.69 μm, seven shortwave channels from 3.7 μm to 4.6 μm, and twelve longwave channels from 6.7μm to 15 μm. The IFOV per channel is about 0.7°. HIRS’s information data along with data from AMSU instrument is used to compute the atmosphere’s vertical temperature and humidity profiles from about 40 km above the land surface. Due to the HIRS’s data is possible to estimate the temperature of the oceans, ozone levels in the atmosphere, amount of precipitated water, cloud height and coverage and the energy radiated by the Earth’s surface. ITT A/CD, same as the previous one, manufactures HIRS/4. 

!{width: 50%}HIRS.png!

Figure XX:

3. ADVANCED MICROWAVE SOUNDING UNIT-A (AMSU-A)

AMSU-A scans the energy radiated at microwave frequencies every 8 seconds. Also,  it has an IFOV of 3.3°, which let achieve a special resolution of 48 km at nadir. As previously mentioned, the AMSU-A’s results are used together with the HIRS/4’s data to calculate atmospheric vertical profiles. Two independent modules, called AMSU-A1 and AMSU-A2, compose the instrument and they consist of 13 and 2 channels respectively. Both modules are shown in the image below.

!{width: 50%}AMSU.png!

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4. MICROWAVE HUMIDITY SOUNDER (MHS)

MHS is an instrument recently added to the NOAA-N’s payload and its main function is to obtain the atmospheric humidity profile, as for example, the liquid water contained in clouds. MHS has five microwaves channels; four of them are humidity-sounding channels from 157 to 190 Ghz, and the last is a surface-viewing window channel around 89 Ghz. This instrument has about 16 km of special resolution, which is higher than the resolution achieved by AMSU-A. It was fabricated by EADS Astrium Ltd via EUMETSAT.

!{width: 50%}MHS.png!

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5. SOLAR BACKSCATTER ULTRAVIOLET RADIOMETER (SBUV/2)

SBUV/2 is an instrument composed of two modules: Sensor Module and Electronics Module. Its main functions are the measure of the concentration, vertical distribution and photochemical processes at the atmospheric ozone layer, and it also measures the radiated sun energy in the frequency range of 160-400 nm. SBUV/2 is made by Ball Aerospace.

!{width: 50%}SBUV.png!

Figure XX:

6. SPACE ENVIRONMENT MONITOR (SEM-2)

SEM-2 consists in three modules: Data Processing Unit (DPU), Total Energy Detector (TED), and Medium Energy Proton and Electron Detector (MEPED). The latter two are sensors, the first of which measures the intensity of particles in the range of 0.05 to 20 keV and the second sensor measures protons, electrons and ions in the range of about 30keV-6.9MeV. Therefore, SEM-2 supplies the intensity and flux of the Earth’s Van Allen radiation belt.

!{width: 50%}SEM-2.png!

Figure XX:

7. DATA COLLECTION SYSTEM (DCS/2)

The DCS is a device that receives data from data collection platforms of the earth in the frequency range of 401 610-MHz to 401 690-MHz. The data are transmitted to the satellite in real time and the satellite, which sends the data once per orbit, receives and stores them for later retransmission to the NOAA Command and Data Acquisition (CDA). CDA stations are located in Virginia and Alaska. From there the data is transmitted to earth processing centers, which are located in Maryland and Toulouse. The data extracted from this process are environmental measures, such as, pressure or temperature of land surfaces, as well as, position or activity of ships and animals. Therefore, these data have many different applications.

!{width: 50%}DCS.png!

Figure XX:

8. SEARCH AND RESCUE (SAR) INSTRUMENTS

There are two SAR instruments on-board the satellite: the Search and Rescue Repeater (SARR) and the Search and Rescue Processor (SARP-2). Both of them belong to the international COSPAS SARSAT system, which main function is to provide assistance in emergencies.  COSPAS SARSAT system works at 121.5 MHz, 243 MHz, and 406 MHz by using Emergency Locator Transmitters (ELTs), Emergency Position-Indicating Radio Beacons (EPIRBs), and Personal Locator Beacons (PLBs).

After receiving an emergency signal, the device SARR transmits a downlink frequency of 1544 MHz to the Local User Terminal (LUT) on the Earth, which must be in view with the satellite to be able to receive this signal. SARP-2 provides a global detection at 406 MHz by retransmitting the emergency signal to the LUT in the same way as SARR does.

Finally, the LUT receives the information and transmits it to the Mission Control Center (MCC). The MCC processes the signal and alerts the appropriate Rescue Coordination Center (RCC), which is in charge of the rescue work.

!{width: 50%}SAR.png!

Figure XX:

9. DIGITAL DATA RECORDER (DDR)

The DDR records and stores the measured values for the following three devices: TIROS Information Processor (TIP), AMSU Information Processor (AIP), and Manipulated Information Rate Processor (MIRP). The DDR belongs to the Command and Data Handling subsystem, which its responsible to transmits the information to CDA’ stations after storing the data during each orbit. In order to perform the storage function, it has two memories. These memories are Dynamic Random Access with a capacity of 1.2 Gbits per DDR. L-3 Communications is the company that made this devices.

!{width: 50%}DDR.png!

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h1. 4. Downlink transmission data from POES satellites

SPACECRAFT DATA COMMUNICATIONS

The NOAA satellites have three different protocols to transmit data to the Earth: Command and Data Acquisition Station Downlinks (CDA), Direct Broadcast, and Search and Rescue.

1. Command and Data Acquisition Station Downlinks (CDA)

NOAA satellite transmits two different types of data signals to the CDA stations. The data signals are called GAC and LAC. 

The first one GAC carries all information data related to one full orbit that is about more than 100 minutes of recorded data. The data contains information about satellite housekeeping, AMSU, and 4 km of resolution AVHRR imagery. [ref].

LAC data signal transports the approximately 10 minutes information recorded by the 1 km AVHRR imagery. If the satellite is within of the footprint coverage, CDA stations can receive real-time information from the satellite.

!(bandwith 50%)CDA.ONG!

2. Direct Broadcast Downlinks

p(. 2.1 High Resolution Picture Transmission (HRPT)

HRPT transmits information data from the whole set of instruments onboard the NOAA spacecraft to all Earth Stations within the footprint coverage.

The TIROS Information Processor (TIP), the AMSU Information Processor (AIP), and the Advanced Very High Resolution Radiometer (AVHRR/3) compose the set of instruments. In addition, the TIP instrument takes data from the High Resolution Infrared Radiation Sounder (HIRS/4) , the Space Environment Monitor (SEM-2), the Data Collection System (DCS/2), and the Solar Backscatter Ultraviolet Radiometer (SBUV/2). Also, the AIP device uses data from the AMSU-A and the Microwave Humidity Sounder (MHS) instruments.

People can have easy access to the NOAA data by buying the equipment formed from a pc, an antenna and a specific software.

p(. 2.2 Very High Frequency (VHF) Beacon Transmission

People get the NOAA data from VHF beacon transmission as a simple way due to the lower data rate of the TIP. Therefore, the equipment required is simpler and users can work with less expensive and complicated technology. The data rate is 8.32 Kbps and the beacon signal is transmitted at 137.35 MHz or 137.77 MHz. [refX]

p(. 2.3 Automated Picture Transmission (APT) Data

Like the previous method, APT data are transmitted to ground stations within the satellite footprint coverage. ATP transmits data from the AVHRR/3 with a 4 km resolution. The transmitted signal is analogical ("Consisting of an amplitude-modulated subcarrier 2400-Hz modulating the RF carrier frequency at 137.1 MHz or 137.9125 MHz")[refX] and it is transmitted from the NOAA satellite through a dedicated VHF link.

After receiving the signal, the Satellite Operations Control Center (SOCC) selects two of the 5 active channels of AVHRR/3 who are called "Video A" and "Video B". Each line of ATP consists of a line of "Video A" and another of "Video B". The auxiliary data is on the edge of each line. Each line has duration of two seconds and it has a repetition period of  64 seconds. [refX]

Due to the simple and affordable equipment required to receive an APT signal, it is common used for academic purposes.

3. Search and Rescue

h1. 5. Current NOAA/POES satellites

!{width: 70%}tablaCurrentNOAA.png(Figure 1.1: Schematic of the different associations)!

Admin=Administration ; Gen=Generation ; TOS=TIROS Operational System; ITOS=Improved TIROS Operational System;  ATN=Advanced TIROS-N; NOAA=National Oceanic and Atmospheric Administration EUMETSAT= European Organization for the Exploitation of Meteorological Satellites