Polar Radar for Ice Sheet Measurements

1
Polar Radar for Ice Sheet Measurements
Polar Science and Advanced Networking Workshop 24
- 26 May 2002

• Motivation
• Project Overview
• Project Objectives
• Science
• Technology
• Communication Requirements

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Motivation

• The Problem
• Long term observed rise in sea level
• Devastating consequences of sea level rise on
  populated coastal areas
• The Need
• Accurate determination of mass balance (the net
  gain or loss of glacial ice)
• Establish a better understanding of internal
  dynamic processes that control mass balance

• The Approach
• Design and develop intelligent radar sensors for
  polar ice sheet measurements
• Implement a mobile data collection system that
  relies on robotics and innovative information
  technology.

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Motivation

• The Anticipated Result
• The data collected and the technology developed
  will enable researchers to
• determine the presence or absence of water
  between the ice and the bedrock
• measure ice thickness and
• map internal layers in both shallow and deep ice.
  
• Which will help earth scientists
• determine more unambiguously how quickly the
  polar ice sheets are melting
• make more accurate predictions of the effects of
  melting on sea level rise

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Project Overview

• Essential Components
• Bistatic/Monostatic SAR
• Dual Mode Radar
• Tracked base vehicle
• Autonomous rover
• Intelligent System
• Communications
• Outreach

5
Project Objectives

• Overall objective is to develop and deploy an
  innovative sensor system for measuring key
  glaciological parameters and studying the
  acquired data to understand the contributions of
  the polar ice sheets to sea level rise.
• Science Objectives
• Measure Ice thickness (DMR)
• Determine Wet or frozen base (SAR)
• Measure Basal water layer thickness (SAR)
• Collect data on internal layer depth and
  geometry (DMR)
• Map bottom topography (DMR)

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Project Objectives

• Technology Objectives
• Develop 3 frequency monostatic/bistatic SAR (60,
  150, 350 MHz) for acquiring data to determine ice
  sheet basal conditions
• Develop a dual-mode radar (Stepped-Pulse/FM-CW)
  for high-resolution mapping of near-surface
  internal layers (100s of meters) and measure ice
  thickness and map deeper internal layers to a
  depth of several kilometers
• Develop a single ice-sheet capable
  manual/automatic vehicle for radar measurements
• Develop near real-time intelligent
  information/image analysis system to dynamically
  select optimum sensor configuration

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Project Objectives

• Technology Objectives (contd.)
• Develop control capabilities for sustaining the
  sensor system, collecting and processing data and
  transmitting it to a central archive
• Integrate vehicles and sensors and evaluate the
  integrated systems at a test site in the
  continental U.S.
• Collect data over test sites in Antarctica and
  Greenland to demonstrate the operation of the
  sensor system and its ability to measure key
  geophysical variables
• Develop numerical electromagnetic and
  geophysical models of ice sheets to specify
  sensors and interpret measured data.

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Communication Requirements

• Three Networks
• Communication within a Vehicle (Intra-platform)
• Communication between the two vehicles
  (Inter-platform)
• Communication from test location back to KU
  (Outreach)

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Intra-Platform Communications Tracked Vehicle
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Intra-Platform Communications Rover
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Inter-Platform Communications

• Need a reliable wireless communication link
  between the rover and tracked vehicle separated
  by 5 Km
• Communications from rover to tracked vehicle
  needed for radar data, rover sensory data ( fuel,
  vehicle health etc.)
• Communications from tracked vehicle to rover
  needed for control signals for location, movement
  patterns, etc.

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Inter-Platform Communications 802.11b

• Data rates of 5.5 and 11 Mbps achieved using
  802.11 b
• Can provide a dynamic shift in data rates to
  provide to support operation over long distances
• 802.11a is an improved version which can support
  data rates of 54 Mbps
• Decision to use 802.11b products because it can
  support high data rates and also the products are
  readily available in the market.

13
Inter-Platform Communications Amplifiers and
Antennas

• Wireless communication link required over a
  distance of 5 Km
• Power output from 802.11b cards is approx. 15dBm
  (30 mW)
• A path loss of 117 dB coupled with the limited
  power out of the 802.11b card meant that the
  received power would be well below the receiver
  sensitivity
• Thus, the use of amplifiers and external antenna
  is required

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Inter-Platform Communications Amplifiers and
Antennas

• Amplifier is a bi-directional 2.4GHz 802.11b
  amplifier with an output power of 1W, receive
  gain of 20dB and a low noise figure of 2.5dB

Antenna is a vertically polarized omnidirectional
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Outreach

• Data to be transmitted
• Real time Video and images.
• Weather data-Wind speed direction, Temperature,
  Solar conditions
• Vehicle data-Virtual dashboard, Accurate
  position, Vehicle health
• Radar data- Ice Thickness,Snow thickness, Radar
  images of rock-ice interface
• Establish a point-to-point connection between the
  field location and KU.
• Transfer real time and near real time data.
• The PRISM server at KU will be hosted on internet

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Connectivity for Outreach Activities Concept
K-12 classrooms
K-12 classrooms
Internet
Public
ITTC
PRISM Outreach Server
Science community
K-12 classrooms
Field Experiment
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Connectivity for Outreach Activities Iridium

• Iridium coverage is available in Greenland and
  Antarctica
• Available bit rates are limited

Iridium Connection Setup
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Connectivity for Outreach Activities Iridium

• Low Earth orbiting satellites
• Global coverage including Poles.
• 2.4 Kb/s per dial-up connection
• Units are priced around 2000
• Airtime is around 1.25 per minute.
• Relative charge 0.5/kbit/sec
• Obtain increased throughput via Inverse
  Multiplexing
• Logically combine a number of low speed links to
  form a high speed connection
• Use multiple Iridium dial-up connections

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Outreach Iridium Architecture
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Outreach Iridium Multilink Point-to-Point
Protocol
Multi-Linked large capacity Bundle
Field Computer
Receiving System at KU/ITTC
To Upper Layer Protocols
From Upper Layer Protocols
M L P P P
M L P P P
Application PPP Packet
Fragmented MLPPP Packets
Reconstructed PPP Packet
Iridium Low bit rate (2.4Kbps) Point-to-point
Links
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Outreach Iridium Multilink Point-to-Point
Protocol
MLPPP configured as Client
MLPPP configured as Server
Multi-port serial card
Multi-port serial card
Emulating a system at test location
PCI Interface
Emulating a system at KU/ITTC
Null modem cables

• Implemented MLPPP over Linux
• Use of Null modem cables to emulate multiple
  links
• Variable rate connections can be obtained
• Obtain variation of throughput with increasing
  number of inverse multiplexed links
• No delay or data loss