GIS: Got vector, Victor? No, Raster, Roger.

Graphical data comes in two forms: vector and raster.  Vector data is composed of mathematical points, lines and polygons.  Since the data is mathematical, it can be scaled to any level without a loss of quality.

Raster data, also known as bitmap data, is composed of different color squares next to each other.  In the most simplest form, take a sheet of grid paper and color in the squares; that is a bitmap image.  Digital cameras take bitmap images.  When you zoom into the image enough, you will start to see squares.

Satellite and aerial images are bitmap images because they are digital photographs.  A human can look at the image and see the object made by the pixels.  A computer had a harder time since it looks at the pixels on an individual level.  The digital photograph must carry meta-data so the computer can understand the basics of the image.

Vector images can be converted to raster images.  Just tell the computer how many pixels, and it will handle the rest.  Raster images cannot be easily converted into vector images.  A computer can draw contour lines at differences in hues, lightness and other color characteristics, but otherwise can’t do much.

The difference between raster (or bitmap) and vector images.
Another comparison of raster versus vector.

 

When the Haiti earthquake struck, there was no road map of the country.  This hampered relief efforts because there was no way for international responders to know what was where.  A crowd-sourced project based in Open Street Maps surfaced.  Volunteers around the globe were looking at before and after satellite images of Haiti.  They drew the vector data by looking at the raster data.  They were able to mark the roads, and then add meta-data of the road’s condition, name and other features of importance.  This was collaborated online and downloaded directly to responders’ GPS units.  The GPS units were able to use this data to navigate the responders.  This was continued to be enhanced by loading in building names and layouts prior to the earthquake.  Now an accurate pre- and post- map exists of Haiti.

It is better to have accurately captured vector data that is loaded with the meta-data.  However, much of the source data that exists is raster information so there are conversions occurring.  Converting data either way between raster and vector creates a margin for error and inaccuracies.

It is a good idea to check the data you are using against the source data.  A common example is when a road’s vector doesn’t exactly line up well with the raster satellite image of the area.  Raw satellite imagery doesn’t include an overlay of the geographical coordinates.  Either the system or a person must anchor the image to a geographical location.  While the center may be exact, the edge can be slightly off due to the angle of the satellite to the surface plane.  This means that we can’t be certain if the variation is caused by an error on placing the satellite image or an error on the location of the vector.  These errors are often small and most people won’t notice them … BUT it depends on the level of accuracy needed in the map.

 

GIS continues: Applications and tools in disaster, crisis and risk management.

How far would you walk for a degree change?

This set of images show the difference between a second, a minute and a degree based on an office in Washington, DC.  The office is located at 38° 53’ 52.59’ N; 77° 02’ 29.60” W.  A couple seconds is about the length of a city block.  As you would expect, the North-South points 1 minute apart along a meridian are 1 nm apart.  The East-West points 1 minute apart along the parallel are only .78 nm apart.  Points that are 1 degree apart North-South are 60 nm apart, yet East-West points 1 degree apart are only 47 nautical miles apart.  This approximation is only valid at this latitude because meridians converge at the poles.  Closer to the poles will make East-West point 1 degree apart closer.  Closer to the equator will make East-West points farther apart.

One second changes.

 

One minute changes. N/S points are 1 nautical mile apart. E/W points are .78 nautical mile apart.

 

One degree change:. N/S points are 60 nautical mile apart. E/W points are 47 nautical mile apart

 

I’m sure that all this talk about degrees, minutes and seconds has made you wonder why there are 60 seconds in a minute, 60 minutes in an degree and 360 degrees in a circle.  We have the Babylonians to thank for that.  They used a base-60 numeric system (sexagesimal) that is used in both time measurements and angles.  You are familiar with a based-10 numeric system (denary), and maybe a base-16 (hexadecimal) if you program computers.  Latitude and longitude are minutes of an arc that originates in the middle of the Earth.

Sexagesimal numbers would name each place past the point in Latin: primus, seconde, tierce, etc.  Minutes are the first position.  Second position is 1/60th of a minute, or seconds as we call them.

While we are off topic, there are 24 hours in a day because the ancient Egyptians used sundials that showed 10 parts day, 12 parts night, 1 part morning twilight, and 1 part evening twilight.  The Egyptians used a base-12 numbering system so it was natural to break day and night each into twelve parts on the sun dial.  Although hours were not the same length of time until the Greeks got involved.

Has anyone ever come up to me in a disaster and asked why our time is a base-60 numbering sequence?  Well, no.  But it is handy knowledge where you’re at a cocktail party, the conversation is in an uncomfortable silence, and you have nothing else to say.

 

GIS continues: Layering on the data

GIS: Laying on the data

We can identify a location on a map using latitude and longitude.  Remember there are other ways to identify a location.  The US National Grid system is the Federal Geographic Data committee’s preferred method.  Amateur radio operators use the Maidenhead Locator System.  Technology today allows the coordinates to be converted from one system to another.  Just be very clear what coordinate system you are using and conform to accepted standards when writing out information.

Our world is physical.  All objects that you can touch have a location and take space.  You can interact with these, such as buildings, roads, mountains, water features, ground features and vegetation.

Objects also have non-physical properties, such as information about the object.  This information could be age, value, names, messages — anything that isn’t physical.  Inputs, outputs, relationships, risk are other non-physical features.

Think of people.  We all have physical characteristics that can be used to define us: height, weight, shape, color, strength, flexibility, etc.  We also have non-physical characteristics that can define us: intellect, emotions, spirituality, productivity, leadership, social networks, financial value, etc.

Both physical and non-physical characteristics of objects interact with other objects.  These can be textually explained but may be better understood with a graphical representation.  I could provide you a list of buildings and their floor space, but you may more quickly see the differences if we overlaid the plans of the buildings so you could roughly compare floor area and outer dimensions.

There is evidence that Cro-Magnon people drew animals and migration routes more than 15,000 years ago.  Dr. John Snow used mapping to study a cholera outbreak in London in 1854.  He drew a map of the neighborhood, drew points for the location of individual cases, and drew an X for the water pumps.  It was easily visible there was one pump in the middle of the outbreak.  Dr. Snow simply removed the handle from the pump and stopped the outbreak.

Original map made by John Snow in 1854. Cholera cases are highlighted in black.

Modern GIS is dependent on geocoding data and layers.  A complete database combined with solid analysis tools allows the leap from map making to true GIS analysis.  GIS is all about the relationships and space of data in the real world.

Layers were easier to describe when most people were familiar with acetate sheets (clear overhead transparency paper).  Imaging a stack of clear sheets where each sheet contained a different set of data.  The very bottom sheet was a base map.

A base map can be referred to as the common data, or the part of the map that you don’t need to create.  It can be the base geography, yet still up for debate.  A base map can be the geographic, demographic or topographic information that services as the common base.  ESRI lists the following as examples of base maps that may be selected: World Imagery, World Street Map, World Topographic Map, World Shaded Relief, World Physical Map, World Terrain Base, USA Topographic Maps, and Ocean Basemap.  In reality, the base map is just another layer that can be turned on or off.

Each layer contains a specific set of related data laid out by geographic coordinates.  Examples of different layers can be transportation systems, gas, electric, water & sewer, telecommunications, terrain, vegetation, buildings, hydrology and subsurface geology.

Layers will be turned on and off depending on what the end-user needs to see.  If I’m interested in the terrain and vegetation to predict wildland fire movements, then hide utilities since they won’t make a difference to the major motions.  A good GIS person will show major water features and highways as they will provide some fire breaks.

Just as the world exists in three dimensions, so can your layers.  Including the elevation (or height) in the geographic data will show the volume of something.  When modeling a hazardous plume, it can show if the plume is at the surface or above the population.  As Dale Loberger pointed out to me: flood analysis, plume dispersion or volumetric surface measures should be done in 3D.  Using technology to display a 3D model that allows you to view from many angles will hopefully reduce your urge to request a printed map when you really need an analysis tool.  Think of GIS as a visual interactive database.

Layers can also include time and historical elements: the fourth dimension (4D).  Historical data can be used to show the growth or shrink in a feature.  The wild land urban interface is an easy example.  Imagine that a community evaluated their risk and models a wild land fire near their community 10 years ago.  Today, their community has expanded yet the prediction has not been updated.  A map of three layers can be used to show what assumptions have changed.  The layers would be the community 10 years ago, the wild land fire prediction, and the community today.  Areas of rapid growth expansion will show.  Small roads 10 years ago may have been widened which may impact the direction and spread of the wildfire.

If earthquake research is my thing, then definitely keep the hydrology and subsurface information.  I’d like to see if the buildings in the community are built on solid footings, or if the ground will liquefy.  Once the major movement areas are identified, then add back the utilities to see where they cross higher risk areas.

 

 

GIS Continues: Vector and raster data types

Getting grounded in GIS: Map making

GIS starts with mapping.  Map making is cartography.  The earliest known map is dated 6,200 BC: a Babylonian clay tablet recovered in 1930 that depicted district boundaries, hills and water features.  Mapping helped to advance human knowledge because it was a new way to capture and share information with each other and future generations.  Passing information to future generations is a basis for developing culture.

Maps of the stars are also maps.  Caves with dots on the walls that represent stars have been found as old as 16,500 BC.  There are other drawing of caves older than the 6,200 BC tablet that represent mountains and rivers.  It is hard to determine if these older drawings of Earth were actual geographic features or just drawings.

I often joke with GIS professionals that they just make pretty maps.  In reality, GIS professionals take a large three-dimensional object (known as the Earth), merge it with data sets through geo-coding, and then provide it to customers in an easy to understand two-dimensional image.  Computers that run GIS are often the most powerful systems in an office because of the large data sets, complex graphics, and significant calculations to perform.

Mapping’s inherent challenge has always been to take a three dimensional object and project it in two dimensions.  A map can provide information on area, shape, direction, bearing, distance and scale.  However, every projection distorts some properties to keep others accurate.  There is no two-dimensional projection that accurately captures all properties of a three-dimensional object.  It is important to select the best projection for the information that is needed.

How hard is it to convert a 3D object to a 2D representation?  Next time you are peeling an orange, try to get the peel off in a few large sections.  Flatten the orange peel.  You will see it stretch, twist and rip as it goes flat.

When mapping smaller areas — such as neighborhoods and cities — an assumption of flatness can be made.  It does depend on the risk of inaccuracy for the map’s purpose.  A few yards of inaccuracy may be fine for consumer level navigation.  A lower level of inaccuracy may be required for landing airplanes in the middle of a runway.  Property boundary disputes may need accuracy to within a few inches.

Some historically powerful island nations may prefer a Mercator projection to give the appearance of a larger land mass.  Just as with statistics, a projection’s distortion can be used to enhance or diminish a feature.

The Mercator projection is commonly used in maritime navigation because it accurately represents initial the shortest distance initial direct bearing.  The other “feature” of a Mercator projection is the size and shape distortion of objects increasing in distorted scale from the equator to the poles, where land masses appear significantly larger.

Why are they called projections?  Imagine a bare light bulb representing the Earth.  Take a piece of paper and hold it to the light.  The features of the Earth are projected on to the paper.  Holding the paper at different angles or shapes make different projections.  Draw a square, circle and triangle on the light bulb.  Now you’ll really be able to observe the distortion of these shapes.

The Mercator projection is a cylinder shape in parallel with the Earth’s axis.  Maps can be referred to by the projection, or by the property that is accurately represented.  Projection shapes include conic or plane (flat).  Preserved properties include direction (azimuthal), shape locally, area, distance, and shortest route.  There are hybrid maps that blend properties of different maps.  While no properties are kept accurate, it “looks” better and more accurate.  Again, it all goes back to the purpose of the map.

Overlay of three projections to show distortions.
Overlay of two projections to show distortions.

There are a few terms used in mapping and GIS that you need to know.

Latitude (aka parallels): These horizontal lines on a map parallel to the equator.  These can be remembered because you give people “latitude” to get their job done so they can go as far to the sides as possible but that doesn’t include a promotion or demotion.  Latitudes are names 0° at the equator to 90° North or South at the poles.  1° difference in Latitude is just about 69 miles.  Except for the equator, a circle of latitude is not the shortest distance between two points.

Longitudes (aka meridians): These vertical lines on a map go North South.  These can be remembered because of the Prime Meridian.  The Prime Meridian is 0° going through Greenwich, England.  The meridians run from there East or West to the International Date Line at 180°.  One the equator, 1° of longitude is ~69 miles converging to 0 miles at the poles.

Great Circle: The shortest distance between two points occurs along a great circle.  A great circle cuts a sphere into two equal halves.  A great circle is the largest circle that can be drawn on a sphere.  All meridians are great circles.  The only parallel that is a great circle is the equator.

Nautical Mile: One minute of latitude along any meridian is a nautical mile.  One nautical mile = 1.85 kilometers = 1.15 miles = 6076 feet.  Note that meridians are used because the distance along parallels change.  The distance along a meridian is the distance between parallels.

 

GIS continues : How far would you walk for a degree change?

Are you reaching the public or just sending notifications?

Public notification is successfully informing the public as to what is going on during an emergency.  The key to reaching people is to reach them timely; where they are; how they want to be reached; with positive actionable information; and in a culturally appropriate manner.

Timely: Information could be too late to be useful if it takes too long to reach them or the information is out-of-date.  Imagine if a building fire alarm took 10 minutes from the time the alert is sent to the time the alarm started to ring.  A building fire alarm needs to ring quickly to give people more time to evacuate the building.  A wildland fire evacuation notice is very similar; the fire moves extremely quickly and can change directions unexpectedly.

How they want to be reached:  Think of how you interact with your family and friends.  Some you will call by phone, some email, some text message and there may even be a few that you mail a real letter to.  You might even admit to have the crazy relative that you’d rather talk to their spouse and have the message passed along.  The public is the same way: all different.  This means that your message must use many different methods to reach all the audience.  Some will want text messages to their cell phone; some will want a voice call to their land-line phone; some will want an email; and there may be a few that are only reachable through the community or faith leader.

Each medium needs to convey similar information, but it need not be the exact same words.  Why should you limit the email to 140 characters just because Twitter is one of many mediums?  For convenience and speed, a message might have a long version and a short version.  The short versions could cover Twitter, SMS, and other short message forms.  The basic information would be shared, along with where to get more information.  The long version could cover email and voice calls.  It would start with the basics and then provide the additional information.

Many of the emergency messages that would be sent can be pre-scripted with blanks left for the immediate details.  Consider the weather watches and warnings.  These are scripted messages that contain all the ever-green information with spots to insert timely specific weather details.  Use the time before an emergency to word-smith the message and get necessary approvals on when it will be used.  Trying to get multiple approvals to send an emergency message is contrary to sending a timely message.

Where they are: This can refer to two places.  Where someone is geographically, and where someone is in the mentality of readiness.

A thing that bugs me is signing up for weather alerts by zip code or locality.  I still get weather alerts for there even when I travel elsewhere.  I want to sign up for one system that follows me.  It can already happen with weather alerts through mobile apps, but it doesn’t happen with local EM alerts.  I have hope that CMAS is changing this.

I live in Fairfax, VA and work in Washington, DC.  I’m registered for county-level alerts in Fairfax, VA; Arlington, VA; and Washington, DC.  Why do I have Arlington, VA alerts?  Because I commute through Arlington and this gives me information on my path.  This becomes amusing on metropolitan-wide alerts as I can see which system sends the information out first and which one takes the longest.

When I travel to another city, I do not get local alerts for that city.  I still get the other alerts from home which is fine so I can take actions to protect my family and property.  When travelling I could do my research, find the local alerting system and sign up for it; but let’s be honest, that’s too much work.  The capability exists today using a feature called “cell broadcast.”  An SMS alert message is point-to-point.  It originates somewhere and goes directly to the single recipient.  SMS alerting requires lots of individual messages all containing the same information which can bog down systems.  Cell broadcasts are point-to-area messages.  It originates somewhere and is broadcasted out to all the phones in a specific area, usually by cell tower.  This doesn’t overload the system because it is one message to many phones.  The technology is commonly used in Europe.  Use in the United States is very limited because it originally released as a way to do local advertising.  Pass the front of a store, and you’d get a text message with a coupon or ad.  People were naturally against this and cell broadcasting has been minimized in the US.  The feature is hard to find on most phones in the US, and defaults to opt-in with no channels loaded.

People also need to be reached where they are in their mentality of readiness.  Telling someone to use their emergency preparedness kit isn’t helpful if they don’t accept the fact they need to have one.  Someone may have a fatalistic attitude of there’s nothing I can do or it is God’s will.  The message needs to be crafted in a way to reach these people where they are mentally.  This leads right into the next point.

Positive actionable information: I chuckle when I hear someone say don’t forget or don’t panic.  How do you not do something?  Mentally, you must flip the message around to figure out what you need to be doing.  That assumes the person reading the message would know the opposite you’d expect them to know.  Craft the message to be a positive action message so the receiver will know what you want them to do and give them something to focus on.  The two statements above should be remember and stay calm.

I forget this all the time in parenting.  I tell my kids things like: don’t touch that, stop making that noise, don’t go over there; instead of keep your hands in your pocket, stay quiet and stay over here.  People should be told what to do, not what not to do.  Messages in a disaster should be simple and direct to be quickly understood and acted on.

Culturally appropriate: Being culturally appropriate starts with using the right language.  Keep in mind just because someone speaks another language doesn’t mean they are literate to read materials written in their native language.  A common mistake I hear is when people say they’ll make print materials in Spanish to reach a Spanish-speaking audience.  Reading and speaking are different things.  A native Puerto Rican told me that he’d rather distribute our materials in English then Spanish.  Apparently, it is easier to understand materials written in English than materials written in European Spanish because Puerto Rican Spanish is that different.  European Spanish— or Castilian Spanish — is commonly taught in academics and is the default Spanish when asking for a translation.  The lesson here is to ask someone from the community the best way to provide written or auditory materials to the community.  Translate to their specific dialect.

Culturally appropriate also refers to the sensitivities of the people.  Migrant farm workers are sensitive to the immigration status of themselves, their family or their friends.  Consider FEMA assistance to these workers before or after a disaster.  The workers will see the DHS logo on the materials.  Who else does DHS have?  U.S. Immigration and Customs Enforcement.  Do you really think that people who are sensitive to their immigration status want to engage with any DHS offices?

Some communities get all their trusted information from a community leader.  Information from other sources may not be readily accepted by the community and have less impact.  Public notifications to these communities need to involve and go through the community leader.  Individuals don’t have relationships with organizations; individuals have relationships with individuals who represent an organization.  Think about it for a minute: your best organizational relationships are likely to have an individual or series of people who you’ve built trust with.  That will be a key when we talk about social media: how do you make your organization interact with individuals on the individual level?

Next time you write a public notification, check off the points I listed above and see if you can improve the effectiveness of the message.

Satellite Comms and Antennas

Satellite Communications

Satellites provide a valuable link during disasters since it requires no local terrestrial infrastructure beyond where you are setting up.  Cell phones require cell towers within a few miles to be working and not overloaded.  Wireline services require a connection through the disaster to where you are.  Satellite systems do require a power source.  Depending on the size, it can be a vehicle’s 12 volt power outlet, a portable generator or a vehicle mounted generator.

A satellite is in an orbit around the Earth.  There are many different ways to position a satellite in orbit depending on the need.  A common orbit for communication satellites is a geostationary orbit 22,236 miles above the Earth.  Precision is needed when working with satellites at that distance.  One degree off and the satellite will be missed by 388 miles.  That is like aiming to land in Washington DC and really ending up in Detroit or Boston.

Antennas

The antenna used makes a big difference.  Let’s start by looking at a two-way radio antenna.  Most handheld two-way radios have an omni-directional antenna.  That means it doesn’t favor any specific direction so orientation doesn’t matter as much.  This gain in flexibility is matched with a loss in “punch” or sending power.  Imagine a basic light bulb in a lamp with no shade.  It spreads light everywhere.  That’s how an omni-directional antenna works.

What if you want that light to be focused to only project sideways?  Like an all around white light on a boat.  The bulb and the lens are constructed to direct the light in a specific pattern.  This is similar to a high gain antenna.  The main punch of the radio signal is increased perpendicular to the antenna by reducing the energy projected parallel out the top and bottom of the antenna.

Now you want to project light in a single focused direction such as a spot light or flashlight.  The bulb is constructed with reflectors and other features to direct the light.  The same is true with radio antenna.  A directional antenna is also called a beam or Yagi-Uda antenna.  Most of your neighborhood roof mount TV antennas take this form.  A series of metal rods direct the radio waves to a higher focus then the use of a single rod.

Wait, a TV antenna?  I thought those were receiving only?  The neat thing about antennas is that they will receive with the same characteristics as they transmit.  A highly directional antenna is more sensitive and will better pick up a signal from its pointed direction then an omni-directional antenna.  However, if the same signal came from a different direction then where the directional antenna is pointed, then the omni-directional antenna will receive it better.

So why don’t we always use directional antennas?  Think back to two-way radio repeaters.  The repeater’s antenna an example of when you want to broadcast the signal widely.  Directional antennas are good for communications between two known locations.  Onmi-directional antennas are good when you don’t know where the other location is, or it keeps changing and moving the antenna continually is impractical.

Going back to our analogy of light to describe radio waves, now imagine that you need a highly focused light.  A laser pointer; it is designed to send out a highly focused beam of light that can be seen for long distances.  The radio version of this is the satellite dish.  The transmitter bounces the signal off a parabolic reflector which theoretically sends all the energy in the same direction in a narrow beam.  These very narrow focus antennas are called “very small aperture terminal” (VSAT).

This series of examples is just discussing the shape of the antenna relative to the direction and focus of the radio waves.  It is possible to use practically any frequency with any shape of antenna so long as the antenna is properly tuned.  Different radio bands are naturally more efficient for communication modes when combined with certain types of antennas.

The important thing to remember here is just because you can do something doesn’t mean you want to do it.  This is where you need to rely on your radio technicians to design the most effective system using the right frequencies and modes to get the message to the final destination.

 

Additional readings

 

Getting a little more technical on satellites

You’ll probably want to start with the entry on satellite communication and antennas before this one.

Orbits

Orbits are put into four levels based on altitude.  Low Earth Orbit is about 100 miles to 1240 miles.  The short distance allows low-power devices with omni-directional antennas to be used.  The most common example is satellite phones, like Iridium.  These satellites circle the Earth in 90 minutes.  From any spot on the Earth, the satellite will only be visible overhead for 10 minutes.

Being visible isn’t referring to seeing it with your naked eye.  Visible means a direct line-of-sight view of a spot so communications can occur.  It also assumes a large sky, such as being in Montana or the open ocean.  The more clutter blocking the sky reduces the satellite visibility.  This includes hills, mountains, trees, buildings and other obstructions, or being in a low spot like a valley.  It is nearly impossible to use satellite equipment in downtown New York City at ground level due to all the buildings.

Medium Earth Orbits are 1240 miles to under 22,236 miles.  At this altitude, the satellites orbit the earth in four to six hours.  That extends the visibility overhead to about two hours.  GPS satellite operate in this orbit.

Geosynchronous Orbits are satellites at 22,236 miles.  It takes a full day to orbit the Earth so the satellite will appear in the same spot of the sky once a day.

Geostationary Orbits are satellites at 22,236 miles and parallel to the equator.  Since the satellite is moving at the same speed the Earth is rotating and in the same plane as the rotation, the satellite is in the same spot of the sky all the time.  This is the most popular orbit to park a satellite in.

High Earth Orbits are satellites above 22,236 miles.  They are not commonly used for our purposes.

Footprints, beams and look angles

A satellite’s footprint is the circular area on the surface of the Earth that is visible to the satellite.  This is the potential area of coverage that the satellite can communicate with.  Areas directly under the satellite will receive a stronger signal then those on the fringe areas due to the increased distance and atmospheric interference.

Satellite operators want efficient use of their equipment so they use beams, or specifically focused transceivers, to cover areas within the footprint.  Imagine a satellite positioned above the equator roughly centered on the United States.  The satellite operator’s intended audience is maritime users.  They would focus the beams toward the waters of the Atlantic, Pacific, Gulf and Great Lakes; and away from inland areas knowing that there are few oceangoing freighters in Colorado.  No energy is wasted trying to fill a part of the satellite’s footprint where it will never be used.  When evaluating a satellite for use, you need to consider the beams and not the total footprint.

The more transceivers a satellite has, the more traffic it can handle at simultaneously.  Satellite operators rate their satellites by the total cumulative traffic it can handle simultaneously through the entire satellite.  The other factor when evaluating service is how much traffic a specific beam can handle.  In normal daily use, it is hard to overload a single spot beam as the resources are geographically dispersed.  A catastrophic disaster will bring many of these resources to a single geographical location; all trying to use the same beam.  That is when the beam will be overloaded.

Outages and overloads on satellite services are common during major hurricanes such as Katrina, Rita, Gustav and Ike.  This is most common on shared satellite services.  Consider the satellite user density that occurs with the convergence of local, state and Federal responders; media and observers; utility companies restoring service; private companies COOPing; and NGOs, CBOs and FBOs responding as well.  Many of these rely on some form of satellite service.  Paying for dedicated satellite airtime is quite costly especially when they only use it occasionally.  Now that a disaster has occurred, they all want to use it at the same time.  In many ways, a satellite in orbit is similar to a cell tower: they are designed to maximize revenue efficiently for normal use, and extreme circumstances quickly exceed the designed capacities.

Finding a satellite in the sky is done through look angles.  These measurements are unique based on the observer’s location.  With geostationary satellites, the look angles will remain constant so long as the observer’s location remains constant.  A look angle is made up of three parts: the azimuth, elevation and polarization.  The azimuth is the compass direction (0-360°).  The elevation is how high to look up (0-90°).  Polarization is rotating the transmitter to align the radio waves with the satellite.

Here’s an exercise.  Imagine that we are using Intelsat’s G-18 satellite located at 123° West.  This is a geostationary satellite so we know that it will be above the equator and 22,236 miles up.  123° West is near the California coast.  If we are in San Francisco, the azimuth would be 180° and elevation 46°.  The higher the elevation, the easier it is to clear tree and other obstacles.  Move to St. Thomas, USVI; the azimuth is 258° and elevation is 22°.  St. Thomas is an island with hilly peaks in the middle so a satellite shot is unlikely from the NE side of the island due to the low look angle.  Change our location again to Boston; the azimuth becomes 242° and elevation drops to 19°.  The same situation occurs in Maine where the elevation is very close to the horizon.  We were lucky during an operation in Maine and setup headquarters at a military airbase that had a runway near the same angle we needed.

Bands and frequencies

Just as two-way radios have a number of different bands with difference characteristics, so do satellites.  Satellites operate at higher frequencies then two-way radios.  A number of these frequencies are shared with terrestrial services.  For example, the S Band (2-4 GHz) includes both satellite radio (Sirius), and Wifi and Bluetooth signals.

Inmarsat BGANs operate on the L-band (1-2 GHz).  These are small, easy to point and decent global coverage.  The major issue with BGANs is the low data throughput (32 to 256 kbps) and high cost.

C-Band (3.7-8 GHz) is well known for the “direct to home” TV signals using larger dishes of 2 – 3½ meters in diameter.  The downside is that C-band has power restrictions and receives interference from microwave services.

Ku-Band (12-18 GHz) doesn’t have the power restrictions of the C-band and is used by the DirecTV system.  The main challenge of Ku-band is the nearness to the resonant frequency of water.  This means that water absorbs radio waves reducing the strength of the signal.  This is commonly called rain fade.  If you have DirecTV, you’ve experienced this when your signal goes out during heavy rain storms.  The wavelength absorption peaks at 22.2 GHz.  For non-technical purposes, think of it this way: The subscript U representing being under this peak.  The subscript A of the Ka-band represents being at or above this peak.

These characteristics are important considerations depending how satellite service will be used.  A Ku-band service will not help you for communications during the storm, but it will have the fastest speeds before and after the storm.  The C-band could work in the storm, but the size of the dish makes portability unlikely and temporary setups risky in high winds.  L-band will get through nearly all the time, but only a relatively slow speeds and high cost.

 

Additional resources

 

Radio types and bands

Radio Types

The simplest radio is the analog radio that transmits and receives on the same frequency.  All radios build from this model.  Imagine two people standing apart, each with a simple radio and antenna.  When one talks, the other listens; and vise versa.

Radio operators wanted to get more distance from their equipment.  Repeaters came into service.  A repeater can rebroadcast (or repeat) a transmission from a higher tower, at a higher power and over a longer range.  The radio operator will transmit on frequency “A” while the repeater listens on frequency “A”.  The repeater rebroadcasts the transmission on frequency “B”.  Other radio operators will tune to frequency “B” to hear the broadcast.  Each radio will transmit on one frequency while receive on a second.

Analog radios transmit the operator’s voice directly by modulating either the frequency or amplitude depending on the mode.  Digital radios encode the operator’s voice into a binary pattern.  The binary pattern modulates the radio signal.  This allows a digital radio to receive the binary pattern and convert it back to voice more clearly than an analog radio.  Interference to the digital radio signal is less likely to influence the quality of the signal.  Digital radio signals can also carry non-voice information.  These include radio handset identification, unit numbers and location information.

In the past, public safety departments would acquire many different frequencies to cover all their projected needs.  They may set aside frequencies for major incident coordination, training, and secondary activities.  Unfortunately, these were also seldom events that occurred only a few times a year.  This lead to a waste of resources to maintain the frequencies and the additional equipment.  A trunked radio system separates the concept of a radio channel from a specific frequency.  One frequency is designated as the control channel while all the other frequencies are open.  All radios monitor the control frequency to get digital control signals from the central coordinating system.  A user would never listen to this frequency as it is all digital control signals for the radio to use.  A user may dial a channel called “dispatch”.  The radio checks to see which frequency is currently assigned to the dispatch channel, and then tunes that frequency for the radio operator.  Meanwhile, the radio will monitor the control channel in the event the dispatch channel changes frequency.  If a radio is set to a channel that has no traffic, there will not be a frequency assigned.  A trunked radio system may have only 20 radio frequencies to serve 100 channels.  The radio of frequencies to channels really depends on how often each channel is expected to be used.

Radio Bands

The frequency spectrum is divided into many bands, or areas of use.  Frequency ranges can be assigned to any number of uses, such as: maritime, aeronautical, amateur, broadcast, fixed or mobile stations, land mobile, satellite, public safety and private/business.  The NTIA frequency allocation chart shows all of these bands color coded.  Some bands have multiple uses yet they’re always very similar, such as mobile satellite and fixed satellite.

The two way radio bands most used in emergency management are private land mobile (which includes public safety and business), amateur and to a lesser extent FRS, GMRS, and CB.

Satellite is another form of radio with a highly focused antenna.  We’ll talk more about satellite frequencies in that section.

 

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Cellular communications

Cell phones are practically everywhere in the US.  83% of American Adults own some kind of cell phone (Pew Internet, http://pewinternet.org/Reports/2011/Cell-Phones.aspx).  These are useful in emergency situations and 40% of American Adults have used them during an emergency.

Most cell phones are low power at .5 watts with an internal antenna.  However, the features of the frequency and other advances allow a single cell site to have a maximum range of 30 to 35 miles in optimal conditions with low user load.  In urban areas, maximum range doesn’t matter as it is more a factor of cell phone density (how many phones per square mile) and building penetration that influences how many cell sites are needed.

A factoid is that a cell tower is not in the center of one cell, but instead on the edge of three cells.  Cell towers are easily identified by the long narrow vertical antennas mounted to a triangular frame so they point in three distinct directions.

Cell sites can also overlap.  A large area may be served by a macrocell.  A high density area within the macrocell may be served by a microcell.  This could be a major interstate intersection, a shopping mall, or stadium — any place where a large number of cell phone users will gather and use their phones.  Individual buildings can install a femtocell, which is a small cellular base station that connects the cellular devices in a building to the cell network through an antenna on the roof or an internet connection.  This is especially useful where buildings are constructed with energy efficient features that block radio waves, or where important section of the build are underground.  Energy efficiency and heat blocking films applied to windows reduce the radio signal passing through the windows.  It is not uncommon to have a great cellular signal outside a building that drops to barely useable inside a building.

During disasters and other unique events, cellular companies bring in specialized units to restore or augment existing service.  Two common units are COWs (Cell on Wheels) and COLTs (Cell on Light Truck).  Cell service was bolstered on the National Mall during the last Presidential Inauguration.  The service providers new that people would making calls, and taking pictures and videos to upload during the swearing in ceremony.  This could have overloaded the existing cellular infrastructure that is designed around normal Mall traffic.

A subtle, yet important, shift from the cellular providers is the placement of branded Wifi hot spots in urban areas.  These Wifi hot spots available at no charge to their own customers shifts load from the cellular network to the wired broadband networks.  Phones from the major providers come preconfigured to prioritize the movement of data across the providers Wifi networks instead of the cellular network when available.  It is a way to load balance the overall system transparently to the users.

Faux G

Cellular systems can carry data as well as voice.  The International Telecommunication Union, Radiocommunication (ITU-R) is responsible for the cellular standards.  The ITU defines what can be called 4G.  Technically, the standard is the International Mobile Telecommunications-Advanced (IMT-A) standard but it is commonly marketed as 4G or LTE-Advanced.  IMT-A dictates minimum data transfer speeds of 100 Mbit/s while in motion and up to 1 Gbit/s while stationary.

You may have not yet experienced these speeds even if your device is labeled as 4G, yet many systems today tout 4G.  In late 2010, the ITU-R gave in to cellular vendors requests and allowed them to use the 4G name if the current system was substantially better then third generation systems and being built to meet the 4G standard.  Resulting from this change, companies went from 3G to 4G overnight because of shifts in the marketing department despite no major changes in the technology overnight.

It is important to take note of the possibility of 4G.  A T1 circuit is 1½ Mbit/s.  The minimum 4G standard of 100 Mbit/s is 66 times larger.  Take a look at the graphic posted on my blog Explaining Bandwidth at http://keith.robertory.com/?p=560 for a better understanding of this.  A cell phone running true 4G will have more bandwidth then an entire site serviced by a T1.  We are right on the verge of a major cellular service shift.  When setting up a site during a disaster, it is common to use one cellular data card (aka aircard) per computer.  With these faster speeds, we can use one cellular data card to be the head of the site’s network.

My team has already successfully setup a network in a disaster with one 4G aircard providing connectivity for 30 computers.  Granted it was rare that there were users on all 30 computers simultaneously surfing the net and streaming large files.  But, that’s the point during disasters — and really even day to day.  It isn’t about providing maximum bandwidth to each user all the time.  Instead, focus on load balancing to provide enough bandwidth to meet the combined average need ~90% of the time.  It is ok for the system to be a little slower during peak demand times.  Set the user’s expectations correctly, and your team will get through it.

A cellular connection could be used to back up a wireline circuit.  Advanced routers can handle multiple uplink connections with prioritization and failover settings.  This will provide redundancy.  It is better than two wireline circuits backing each other up when the backhoe cuts through the utility lines outside the building.  Redundancy is nice.  Diverse redundancy is better.

Your users in a disaster response will be on the computer only part of the time, with the rest of their time filled with other activities.  If a disaster responder travels to a location and spends the entire time behind a computer, then the question should be asked: could that person just stay in the office or at home to complete the same work?

 

Additional resources