About the weather cameras

It may be easier to understand how things work if we started at the back-end and worked forward:

The Back-end

The frame grabber is provided many video channels, from which it can select which one to capture and store as an image.

A program in the the computer controls the frame grabber, telling it which channel to look at, and when to capture an image. It can add a caption to the picture, which might include a name and date stamp when the picture was taken. The program can pull the image off the board and save it as a JPG file on the computer's disc drive.

Another program creates the "All-in-One" web page which uses the JPG files. A third program is used to move all of these files to the web site.

A break-out box outside of the computer, connected by ribbon cables to the frame grabber board, allows many different video channels to be sampled. Coming into the box, all of the channels are "NTSC" video.

Hardware & Software:

• Frame Grabber: Sensoray 617 "PCI Frame Grabber"
• Break-out box: Sensoray 609TA-ND "Video Termination Board"
• Software: The program controlling the frame grabber board was based on its demo program.
• Software: The program which builds the "All in One" picture web page is homebrew, written in "C".
• Software: The program which sends the files to the web site is a simple "batch" file which executes an FTP session.
• Software: A program which coordinates execution of other programs, "cron", is described in the weather station's pages.

The Front-end

• Cameras in the same building as the weather computer send their video output directly via RG-6 coaxial cable.

• Some pictures arrive via the in-area cable TV system. Dedicated (and otherwise retired) VCRs are used as receivers, to convert the TV channels to NTSC video.
  - Two of the channels were provided from the "headend" by the cable system's operator.
  - One channel is injected into the cable system partway down the mountain, using a modulator and a "tap" (being operated backwards), to inject a signal into the cable on a previously unused channel.

• One camera uses a "video modem", which can send a video signal over thousands of feet of simple twisted-pair copper wire.
  - The modem transmitter accepts the camera's video signal and drives a telephone-grade line.
  - The receiver outputs an NTSC video signal.
  The video quality is surprisingly good, though subject to interference when high-power electrical equipment operates near the telephone cable.

• One camera uses a 900 MHz radio link
  - The "hop" is about 2000 feet line-of-sight.
  - This is the newest installation, and we are still learning about what it takes to transfer a good picture.

• Cameras: Sony Handycam CCT-TR940 (great zoom lens; it doesn't time-out), & various "security" style cameras (Pelco CC3701H, . . .)
• Modulator: Blonder-Tongue BAVM-z(?)
• Directional Coupler: Regal RDCT10-6
• VCRs: Hitachi 5-head VHS, RS Optimus Model 107 & 111
• Video modems: Network Video Technologies NV-653T (transmitter) & NV-652R (receiver)
• RF Video link: VideoComm T-906AHPM (transmitter) & CCR-900 (receiver)
• Surge supressor (on the power lines)
• Lightning arrestor (on cable TV lines)

Camera Installation Considerations

1. What is there to see?
   - Things near and far, in case visibility becomes limited?
   - Things which move or change?

2. Where can a camera be placed where it can see, yet be "out of the way"?
   - In the corner of a window?
   - In a box, bolted to the outside of a building or up on a tower?

3. How well can the camera see?
   - Zoom lenses are useful to get just what you want in the picture.
   - Try to maximize the camera's "lines of resolution". Many simple security cameras can be disappointing.
   - Will it be Color or Black & White ?
   - Do you need low light sensitivity ?
   - Will you have a wide range of brightness? (e.g. sun on snow versus dark soil on rainy days) An "auto-iris" might be needed to handle this.

4. Will the sun ever be in the field of view?
   - Allowing a camera to stare at the sun for long periods of time may permanently damage it.
   - During the course of a year, the azimuth of the sun's rising and setting may vary widely. So will its altitude above the horizon. A simple azimuth versus altitude chart for your area (Latitude) might be handy.

5. How will you power the camera?
   - Plug-in, solar powered, ...

6. How do you get its video to the network?
   - Coaxial cable? RF modulator? 900 MHz RF link? Video modem?
   - Frame grabber card, or . . . ?
   - How many camera inputs?

7. Will it continue to operate in various weather conditions and situations?
   - Cold ? -> Heater
   - Hot ? -> Solar shield
   - Fogging, frost -> Window defogger / defroster
   - Rain -> Window wiper
   - Rime icing -> Heater
   - Wind -> Secure mounting
   - Lightning -> Surge/lightning protection on all copper lines (power, TV, video, phone) which enter or leave a building
   - Floods -> Secure support structure for camera, power & video lines
   - Power outage -> Uninterruptible power supply, so hardware (like VCRs & Camcorders) don't lose their settings.

Edits: 2004 09/16,18; 2005 01/02; 2006 02/17