Raja Jurdak, Philipp Sommer, Branislav Kusy, Navinda Kottege,Christopher Crossman, Adam McKeown, David Westcott

Autonomous Systems Lab, CSIRO ICT Centre, Brisbane, QLD, AustraliaCSIRO Ecosystem Sciences, Cairns, QLD, Australia

Junction 2013.04.29

Camazotz: Multimodal Activity-Based GPS

Sampling

Camazotz The Maya’s Bat-God

Camazotz platform: Multimodal Activity-based Localization (MAL)

- detect activities by combining multiple sensor streams

for fine-grained control of GPS sampling times.

Target:

Lightweight, long-distance, and long-term tracking

Introduction track flying foxes (fruit bats) 狐蝠 (澳大利亞特有種 )

1. Spread Ebola, SARS-like Coronavirus(冠狀病毒 ) collection data from highly mobile animals

1. Position information (GPS)2. Activity information (inertial, acoustic, air pressure)

Challenge:1. Sensing modalities: burden on limited node energy, processing and

memory resources2. Uncontrolled 3-D mobility: unpredictable effects on the transceivers, and

solar panels

Detect unknown congregation areas and

roosting camps

Application to understand flying-fox ecology behavior1. Nocturnally active2. Roost in large aggregation (40-50,000 animals at a single

site)3. Highly mobile (travel 20km to their first feeding site in a

night and over 100km during nightly, over weeks and months individuals can move hundreds or thousands of kilometers)

4. Threatened species (agricultural pests)5. Virulent emerging infectious diseases

obtain day roost locations for comparison with surveyed comp locations, and know the group number

Platform target1. Collecting regular daytime fixes (with accuracy of 10m) at

camps to identify new camps

2. Collecting high-frequency nighttime fixes to monitor movement patterns and landscape use, and doing this with an accuracy of 10m or less using inertial sensors during fine scale movements

3. Making daytime audio recordings to allow estimation of camp size

4. Operate over long periods (12 months, and preferably longer)

5. Provide data download capability

Design Challenges1. Size: 2cm x 2cm, 30~50g (<5% animal weight)

Might affect the size of GPS antenna -> accuracy

2. Mobility dynamics: continental scale Cellular coverage may not be available

• Cellular module also add significant weight, size and energy cost Choose to transfer position data by installing BS at known

roosting camps Using short-range radio communication opportunistically

High degree of delay tolerance (memory, data compression, opportunistically deliver once connectivity return)

Hardware TI CC430F5137 (MSP430 core + CC1101 radio) Support low power operation and offer high compatibility with

popular sensor network operating systems.

Zigbee (915MHz band in

Australia)

GPS antenna

Hardware

U-blox MAX-6 GPS

Amplifierdirectional

ity

Smaller antenna’s omnidirectional radiation

-> favorable for the 3-D mobilityAdd 20dB low noise amplifier (LNA)

Less power consumption* Need 12x ground plane

(=overall Camazotz)

Dual side solar panels can harvest energy

during night (up) and daytime (down)

Energy charging architectureFully charged and fully flat -> directly charged from solar panels (bypass circuit)

1. Fully flat: low current -> if from battery -> risk oscillation around a minimum voltage threshold -> data loss

2. Fully charged: can use any excess solar energy for increased sampling or computation

Energy budget: low power sensors

1. Pressure sensor (Bosch BMP085): 12μA

2. 3-axes Accelerometer/magnetometer (STMicroelectronics LSM303): 830μA

3. Knowles microphone + 12bit ADC: <1mA

Duty Cycle-> on average 12 μA overall

Software OS: Contiki

1. RPC (remote procedure calls) to send radio command Perform certain actions (reading memory blocks, status

information) Adjust configuration parameters (GPS duty cyle) Sent by unicast/broadcast packet [command id, arguments]

2. Logging abstraction due to long delay tolerant Test phase: high sampling rate one SD care Deployed phase: adjust sampling rate and log in external flash

card

Evaluation on Mobility Bat-to-BS (3G) near roosting location, bats-to-bat communication outside

Under high mobility (7-8m/s) and surrounding trees to increase PRR

1. Experimental Platform (quad-copter with GPS and inertial sensor) Duration: max. 30min, total 10 hrs, >20km Broadcast pkts(32bytes), 8 pkts/sec BS: 1.5m above the round, 20cm diameter ground plate 3 kinds of antenna (large, small, and simple whip antenna) Log RSSI and PRR for evaluation UAV: send pkt 4Hz to tell GPS location and speed

Evaluation on mobilityAntenna Selection

Smaller is worst

Simple whip antenna outperformsAlmost no packet lossesWith smaller variance of the RSSIdependable

Evaluation on mobility Impact of Speed

No correlation between speeds and the RSSI

No need to constrain packet transmissions based on the speed

Evaluation on mobility Impact of Angle

Only a minor degradation of the signal quality at higher angles

Avoid installing the BS directly under the trees populated by flying foxes

Evaluation on GPS Static outdoor setup Attach Camazotz board to a tree on campus

(when flying fox roosting) After 60 sec a position fix has been acquired,

switch GPS antenna off - keep ephemeris information in RAM

- GPS is able to do a warm start

off time interval: [10s, 60min] measure TTFF (time to first fixt)

TTFF is correlated with the time interval the GPS receiver was

switched off

Evaluation on GPS Attached to flying fox in a large outdoor cage Camazotz log 1 Hz GPS data to its SD card Continuously send status update messages via radio to a BS how to measure the true location

- roosting location

(averaging over 3600 fixes GPS)

- use geo-referenced high resolution imagery

(with a spatial accuracy of 1m)

Calculated (GPS): (M=7.2, SD=1.3)Measured (GG): (M=5.9, SD=3.0)

GPS provide conservative estimates, more cluster

Evaluation on long-term operation log solar charge current at 1 Hz Dips: caused by

shadows from the structure of the bat

enclosure

Lower that static node Non optimal orientation Bat’s habit resting in a

shade

5mA peak: small glimpse of sunlight were caught

Just below 5.7 Mw PER DAYMeet the energy neutral target

3mA 12hr (5.7mW)

Evaluation on activity recognition

Wing beat frequency For height

Fight for territoryMating advances

By distinct sounds

Increased movement

Important to detect:Where they spread

seed

Use Acc to detect motion upside down to right side

up

Use their claws to scratch their

bodies

Typical in upside down position, moving

head/neck

Default status as baseline

Inertial Inversion events was detected by computing the angle θ between the current 3-D acceleration vector c and the inferred gravity vector g

identifying contiguous samples of at least 4 s where the angle was shifted by at least 90 degree

100% accuracy with 3hr trace

Audio In-built microphone 22.4 kHz (mainly within 2 ~ 4 kHz, 8 kHz)Interaction events (mean sound level, call duration, mean normalized frequency) by classification1024 samples window (1/2 overlap), simple threshold

Select 0.002

Mean accuracy 77.5%Mean precision of 70.7%

Air pressure GPS Error (horizontal: 10m, vertical: 20m) instead rely on air pressure sensor use the pressure sensor on the BS as reference altitude

Data average over 1 min time window

Fluctuations in consecutive samples appear to be within 0

to 50 cm

Cag

e

10

0m

Feed

ing

tim

e

Multimodal activity based localization To detect interaction event accelerometer + inertial + audio with angular shift (inversion) duration shorter than urinate/defecation with an initial jerk (bat is agitated) average (54s) -> differentials (high) each peak: vocalization lasting for 5s

43.8 and 60 degree (with highest differentials in average angular shifts) -> inertial jerksThird highest 18 degree -> 30 as threshold

Multimodal activity based localization

When to trigger GPS sampling (simulation)

1. accelerometer only Detect events only from the collared

bat GPS active 21s, 86% power saving

2. audio only All 4 events (can’t distinguish events

nearby) GPS active 64s, 7.42mW power

consumption

3. combination

Conclusion Feature-rich lightweight Camazotz platform for long-term tracking of flying foxes

Comprehensive empirical evaluation in both laboratory and on-animal experiments.