Update of GPS systems technical Update of GPS systems technical specifications and challengesspecifications and challenges

– GPS– Communication– Power

Bjorn JohnsSeptember 7, 2005Polar Technology WorkshopWashington, DC

GPS receiversGPS receiversState-of-the-art in 2005:• Power: ~2W• 1 Gb on-board memory• <$10,000 with DM chokering antenna• Observables: Track all-in-view GNSS satellites, L1, L2, C/A,

P (Y), L2C, GLONASS• Communication protocol: serial and IP• Easy field downloads: removable CF memory or just swap

receivers• Reliability: real-world MTBF > 4 years• Extreme cold environment not a big issue• Mature, commercially available, solid-state, consumer

electronics

Some off the shelf GPS choicesSome off the shelf GPS choices

Topcon

TrimbleNovatel

DM IGS standard chokeringantennas

Dana Caccamise/Eddie Wheeler Tech 2000

SCIGN radome

TAMDEF receiver useTAMDEF receiver use

GPS receiver challengesGPS receiver challenges• All features are not provided in one product – typically

issue a wish-list RFP and make tradeoff decisions• New products are plagued by hardware and firmware

flaws – require rigorous testing, follow-up, and vendor response

• Custom firmware for unique needs of academic community and extreme environment

• Don’t know real MTBF in advance – operational field experience is essential before committing to a particular model in the Antarctic

Communications for GPS summaryCommunications for GPS summary• Why: Data users benefit from low latency data retrieval• Why: Advance knowledge for station maintenance and troubleshooting• Why: Streamlining of downstream data quality control and processing• GPS data volume < 1Mb/day• Adds 1W to power budget• Cost:

– Radio modem $1,500 and no recurring– Iridium modem $1,500 plus recurring airtime cost

• A three-tiered approach for GPS data retrieval:1. Line-of-sight radio links and repeaters proven for IP and serial comms an

Internet node2. Commercial satellite-based connection (e.g., Iridium) if the distance to an

Internet node exceeds the distance capability of radio modems3. Onboard memory will serve as backup in the event of loss of the communication

link, allowing for manual data retrieval during the next maintenance visit or opportunity visits.

Radio communications provenRadio communications proven

• FreeWave radios used by community since mid 1990s

• Transantarctic sites • Mt. Erebus sites• UNAVCO global applications,

EarthScope

Erebus site HOOZ

Mt. Erebus repeater can serve TAM sitesMt. Erebus repeater can serve TAM sites

Iridium communication test at TAMDEF site Iridium communication test at TAMDEF site Fishtail PointFishtail Point

Communications for GPS Communications for GPS challengeschallenges

• Iridium data link reliability – latency, disconnects, and lock-ups

• Custom hardware solutions• Future satellite solutions?• Integrating GPS and seismic state-of-health into

one data link• Keeping on-site “smarts” to a minimum• Managing summer vs. winter comms for power-

saving• System integration: GPS/modems/download

software/delivery to data archive

Autonomous testAutonomous test--bed site built this summer, bed site built this summer, McMurdo deployment planned for October 2005McMurdo deployment planned for October 2005

UNAVCO network monitoring and data archive

On-line data access

Self-contained McMurdo test-bed

Remote site

Remote GPS data collection

Deploy system to field after burn-in

Burn-in and test integrated system, communications link

Radio link GPS data communications flow

Mt. Erebus Repeater

RADARSAT/ Bldg 71 Internet access

UNAVCO network monitoring and data archive

On-line data access

Self-contained McMurdo GPS test-bedVery remote site

Very Remote GPS data collection

Deploy system to field after burn-in

Burn-in and test integrated system, communications link

Iridium link GPS data communications flow

Iridium LEO satellite communications system

Mt. Erebus dataflow from Hooper’s ShoulderMt. Erebus dataflow from Hooper’s Shoulder

CONZ stateCONZ state--ofof--health info health info

Power systems for GPSPower systems for GPS• GPS receiver system total power budget <5W

(GPS, comms, ancillary)• Photovoltaics and sealed lead acid battery

power systems well understood, but heavy and temperature limited– Solar-only “brute force”: 160W PV array, 2700Ah

battery bank for year-round operation, 5W system at 80 deg S ($3500, 2000lb)

• Wind turbines: Promising, used successfully with GPS systems on Erebus and at Mt. Coates

SolarSolarTAMDEF site FLM2

WindWind

Ampair turbine at Erebus site HOOZ

Power systems for GPS Power systems for GPS --challengeschallenges

• Better (and affordable) battery technology: cold performance, energy density

• One-time lithium or air cell batteries for reserve

• Wind turbine reliability, set-up• Power saving measures: near year round

operation, comms only in summer• Insulated enclosures bulk vs. cost vs.

longevity

Insulated enclosuresInsulated enclosures

R-25 big box

Complete systemComplete system

GPS component matrixGPS component matrix

2,400bps2lb$1,5001W Iridium modem

40lb$200Solar panel frame

40lb$700Enclosure

2 lb$35030APower board

15lb$500GPS antenna mount

56kbps2lb$1,5001WRadio modem

25lb$35080WSolar panel

70lb$120100AhBattery

750kb/day10lb$10,0002.5WReceiver w/chokeData rateWeightCost PowerItem

Key GPS technical points:Key GPS technical points:

• No major “extreme environment” problems for GPS sensors

• GPS systems can be readily deployed for “spring-summer-fall” only operation

• Advanced battery technology and reliable wind systems desired for year-round operation

• Thorough system integration, testing, operation and maintenance is necessary for success

• Challenges well within reach of an organized community effort