Site requirements and preparation

An Argus station requires a stable mounting point for the cameras, power, and communications.

It also requires a name. Names are by convention ten or fewer lower case letters (a-z) from the Latin-1 character set (http://en.wikipedia.org/wiki/Latin-1). Digits (0-9) are allowed but not as the first character.

Camera housing and mounting

Argus uses fixed cameras to observe the coast over a long period of time. Camera stability is essential. The cameras should be free of vibrations in most wind conditions (ideally up to and including Beaufort force 8), and the camera should not be subject to diurnal oscillations or long-term sagging. Diurnal oscillations are frequently caused by asymmetric heating and cooling of (parts of) the building or mast on which the cameras are mounted. Sagging is caused by weak materials (e.g., wood) or not properly fastened bolts. A camera is actually more than one component. It needs a lens appropriate for the view, and a watertight housing to protect it from a marine environment and weather.

Lenses are chosen during the design phase based on desired fields of view and availability. Fixed focal length lenses are preferred because of the their simpler distortion modes (see below) and fewer moving parts.

It is best to fit each lens with a UV blocking filter and polarizer. The UV filter protects the camera's CCD (or CMOS) sensor from long-term damage due to the relatively high-energy UV photons. The polarizer reduces glare when the sun is low over the water, or from other reflective surfaces. Some wide angle lenses cannot accommodate two standard filters, in which case an adapter ring to a wider diameter may be used. In some cases a polarizer is sufficient (UV is also polarized).

The camera housing should be IP65 (http://en.wikipedia.org/wiki/IP_Code) or better. In humid environments with significant diurnal temperature differences air flow into and out of the enclosure should be limited to an absolute minimum. If not, liquid water may slowly accumulate in the housings during nighttime condensation. Keeping the relative humidity around the camera low (say below 50%) is best for longevity. Ample silica gel packets placed in the housing is recommended even when the housing is "air tight".

Over time the glass at the front of the housing can get dirty and impair the view. Common source are dried salty spray, fine sand and dust, and bird excrement. Ideally the cameras can be easily reach for periodic cleaning. Usually this is not a problem when mounted on high ground or a building; a short ladder may be useful.

Cameras mounted in masts or towers can be more difficult to reach. One solution is to mount the cameras on a platform that can raised and lowered by hand or electric winch. This makes the mast more complex, however, and care must be taken to ensure that when the cameras are raised they consistently lock into a fixed position. Climbing tall masts requires training, safety equipment and a safety person on the ground. This should be avoided if possible.

Another approach to keeping the glass clean is an integrated washer/wiper system that can operated remotely. Unfortunately this adds complexity to the system, especially when there is a large vertical distance between the washer fluid reservoir and the cameras. (Pump water up much more than 10 m requires powerful pumps.)

In rainy climates, rain will help clean the glass. Some site need very little maintenance.

Power

An Argus station needs power, ideally mains power at 100-240 VAC 10A. Typical power consumption is about 4 W per camera and 150 W for a standard computer, or 50 W or less for a low-power computer. If mains power is unreliable, a UPS with backup battery, transient filtering, and over-voltage protection is recommended. An endurance of 15-20 minutes is usually sufficient. If mains power is not available, solar, wind and other sources can be deployed. This will require low-power components, and perhaps aggressive power management.

The cameras (and hubs and repeaters) run on 12-24 VDC. When mains power is available a good quality AC-DC converter (regulated power supply) is required. 5A is recommend for up to 6 cameras. When the distance between cameras and power supply is longer that 10-20 meters a higher supply voltage is chosen to compensate for voltage loss due to cable resistance.

Communications

The Argus station should be connected to the internet for management, control and monitoring, and to upload collected data.

There are various options:

• A direct, wired connection using existing Ethernet infrastructure at the station location. This requires participation of the site owners/managers, and possibly some configuration changes to their router/firewall. It is possible to limit bulk data transfer to late at night only. This might be appropriate at a hotel or office building where most internet use occurs during the day and evening.
• A new wired connection at the site. Requires participation of an internet service provider.
• A point-to-point wireless link to an existing internet connection in the area. 2.4 and 5.8 GHz Wi-Fi (http://en.wikipedia.org/wiki/Wifi) bridges are cost effective, easy to install and do not require a license in most countries. Distance of up to 25 km can be covered if there are no obstructions along the path. Longer distances require higher antennas.
• A mobile phone internet connection. This should be avoided. Most mobile telecom cannot provide the needed bandwidth at all, or at a reasonable cost.

A mobile internet connection can be used for management of the station in conjunction with removable storage devices for physical transport of bulk data.

Ideally the Argus station has a fixed IP-address or uses dynamic DNS (http://en.wikipedia.org/wiki/Dynamic_DNS) so the archive server can connect to it. If needed the station computer can be programmed to contact the server. Needless to say, attention needs to be paid to security. Normally Argus uses SSH (http://en.wikipedia.org/wiki/Secure_Shell) tunneling, but but other VPN solutions are possible.

Vulnerabilities

Any field measurement station is exposed to certain threats. In the case of an Argus station major risks are lightning and criminal activity such as vandalism and theft. Excessive heat or cold can also be a problem.

Lightning

Lightning is potentially the most destructive threat, and in certain circumstances technically the most challenging to mitigate.

If Argus cameras are the highest objects in the near area lightning protection measures are highly recommended, and essential in lightning-prone areas such as the (sub)tropics. The most basic measure is one or two grounded lightning rods within 3-10 m of the cameras to avert a direct strike. The grounding wire's path - if it runs parallel to Argus cables for more than a few meters - should be at least one meter away to avoid induction currents in the Argus data or power cables.

For metal towers with a good lightning rod at the very top, the current from a strike will flow through the entire tower to ground, so the resulting magnetic fields should not be able to induce damaging current in properly shielded cables.

Extra protection is afforded by running the Argus cables through grounded metal conduit and/or terminating all long cables that run parallel to a potential lightning discharge path with lightning arrestors. (Available for both DC power circuits and gigabit Cat5e/6 UTP/STP (http://en.wikipedia.org/wiki/Unshielded_twisted_pair) data cables.) Lightning protection is a specialized field. Local, expert advice should be consulted if the risk is moderate to high.

Vandalism and Theft

Argus stations placed at publicly accessible locations are vulnerable to people with bad intentions. Motivations can be theft of (perceived) valuable equipment, disruption of image collection, or plain vandalism by drunk or drugged passersby.

Towers at remote locations are at greatest risk. It's best to erect a security fence around the perimeter, and enclose the computer and other ground-level equipment in a secure enclosure within that perimeter. For most locations with a tower up to 25 m a fenced-in area of 10 square meters would be enough. In some countries with strong liability laws the property owner may be held responsible if an unauthorized person climbs in the tower and falls with (fatal) injury.

Extreme Temperatures

Normal Argus components are designed to operate in ambient temperatures up to 50 degrees Celsius. Because they are enclosed, ambient for a component is not necessarily the outdoor temperature.

Cameras in individual metal housings with a sun-shade are not a problem temperate climates. They dissipate less than 4 W and actually keep their environment warm for incidental cold spells (to -10 C overnight). In locales where temperatures can exceed 40 degrees Celsius additional shading and cooling fins are recommended.

Computers - especially normal PCs that run of mains power - could be more problematic when housed in a small enclose without adequate ventilation, especially if exposed to sunlight. Often the power supply for the cameras are in the same enclosure, which adds to the heat load. Various solutions are available.

Cold has not been a problem. Argus stations are located on the coast, with its moderating influence on ambient temperatures. A few consecutive nights at minus 10 degrees Celsius, warming 5 degrees during the day are survivable, provided all equipment remains on and outside airflow is not possible.