AGILE 2016 - SensorWeb Semantics on MQTT for responsive Rainfall Recharge Modelling

Integrating Wireless Sensor Networks (WSNs) and spatial data web services is becoming common in ecological applications. However, WSNs were developed in application domains with different sensor and user types, and often with their own low-level metadata semantics, data format and communication protocols. The sensor web enablement initiative (SWE) within the Open Geospatial Consortium (OGC) has released a set of open standards for interoperable interface specifications and (meta) data encodings for the real time integration of sensors and sensor networks into a web services architecture.
Such XML-based web services exhibit disadvantages in terms of payload and connectivity in low-bandwidth low energy unreliable networks, such as remote 3G uplinks. Monitoring stations deliver frequent measurements in real-time, but dynamic implementation of measurement frequencies, adapted to certain environmental conditions, are rarely implemented. We describe a responsive integrated hydrological monitoring prototype to calculate rainfall recharge for water management purposes.
When rainfall is observed, a threshold event triggers a reconfiguration task for the soil moisture sensors, using asynchronous, push-based communication implemented with an MQTT queue. A Sensor Planning Service commits that request via MQTT into the wireless sensor network, and updates the measurement frequency of the target sensors to gain higher resolution for the vertical soil water infiltration.
The system integrates a Sensor Observation Service (SOS) including field observations and internet-based environmental data with a rainfall recharge model that allows near-real time calculation of rainfall recharge in the Upper Rangitaiki catchment, Bay of Plenty region in New Zealand.

Figure 1: Setup and location of the sensor field site, central North Island, New Zealand

The prototype site comprises a main station conducting comprehensive measurements of meteorological, hydrological and pedological parameters. For the wireless data transmission within the local site installation XBee-PRO modules from the Digi Company  ZigBee IEEE 802.15.4 protocol are used. The main station receives continuous sensor measurements from the attached sensor units, and acts as the gateway to the online SOS and SPS services by providing the communication channel from the local sensor network to the web-enabled data management infrastructure.

The field site has been established in the Upper Rangitaiki catchment (Figure 1) and comprises a field computer (Raspberry Pi) with a direct internet link (GPRS/3G) and a sensor board (Waspmote) that has 12 typical meteorological, hydrological and pedological sensors attached (i.e., wind speed, wind direction, rainfall, 1x groundwater probe, 5x temperature and 3x soil moisture). The Raspberry Pi and Waspmote can be monitored and reprogrammed from an online server.

Figure 2: Raw sensor series visualized in a website from a SOS query.

The site setup allows scaling up to a multitude of low cost, low energy sensor stations throughout the catchment, with only one field computer that serves as data logger for backup. The observations were available in a standardized open format. The website accessed the raw data from the SOS server and plotted data points within 5-10 minutes of field measurement. This website was easily accessible via browsers and smartphones (Figure 2).

The paper was was presented at the 19th AGILE International Conference on Geographic Information Science, 15th of June, in  Helsinki, Finlkand.

Kmoch, A., Klug, H., White, P., & Reichel, S. (2016). SensorWeb Semantics on MQTT for responsive Rainfall Recharge Modelling. In 19th AGILE International Conference on Geographic Information Science. Helsinki.

Amazon IoT and OGC SensorThings vs SOS/SPS on MQTT

Today I stumbled over a blog post on the OGC Blog about "Amazon IoT and the candidate OGC SensorThings API Standard"

It was great to learn that Amazon IoT uses MQTT as network / transport layer. The more interesting is the move towards REST (which is HTTP) to address semantic issues with IoT systems:

AWS IoT, MQTT and many other network interoperability standards (LWM2M, CoAP, etc.) enable message interchange.  However, IoT network interoperability doesn’t enable the systems that are exchanging messages to interpret those messages. To realize the many-to-many system-of-systems vision, IoT applications need to implement standard ways of communicating sensor locations, sensor and data parameters, and sensor instruction sets. This is what the OGC SensorThings API provides.

It is understandable from the point of view, that OGC OWS is in general intrinsically interwoven with HTTP semantics and the application of SWE in the IoT context is desirable, well, even crucial.

However, MQTT stems from the constraints of low bandwidth, low energy consumption and unreliable connectivity, and implements a robust, small footprint asynchronous messaging platform. Earlier this we have developed a prototype system, that aims to add SWE semantics into MQTT messaging. We keep the specialisation of MQTT, where for example connections can be resumed which under SSL/TLS security can be a significant power saver. MQTT would also better address the "addressability" of distributed "things" which might be isolated behind IP NAT or run with dynamically assigned addresses, because in MQTT context the "things" would subscribe to SPS management topics and therefore higher order SDI services don't need to direct data queries or task requests to an address but place it on the queue with respective topics.

For an agricultural research project we distributed monitoring stations as a wireless sensor network throughout the catchment to deliver frequent measurements in near-realtime, which mimics OGC SOS.

A dynamic implementation of measurement frequencies, adapted to certain environmental conditions like heavy rainfall events require re-tasking of the nodes, which mimics OGC SPS. Within this paper we provide a framework where a threshold event triggers a reconfiguration task for a phosphorus measurement device, using asynchronous, push-based communication, on an MQTT queue, which links the ground stations with a cloud-based control system. OGC WPS algorithms continuously analyse incoming SOS measurements commits such a request into the wireless sensor network, and updates the measurement frequency of the target nodes to enable nutrient peak flow estimation during storm events.

This on-going work is based on original thoughts on the  interlinking  of  OGC  SWE  semantics  for  sensor  descriptions  and  observations (OGC Sensor Observation Service, SOS), sensor configuration and planning (OGC  Sensor Planning Service, SPS)  with  the  open  Message  Queue  Telemetry  Transport  (MQTT)  protocol.

MQTT  is  a  simple,  yet  very performing  and  robust  publish/subscribe  message  passing  system,  which  can  also  serve  for  event  brokering as  described  in  the  SWE  Service  Model.  Actual  addressing  and  data  transmission  is  done  by  a  topic  string and an arbitrary payload. The topic string and the payload need to reflect the necessary standard semantics to be  mapped  back  and  forth  to  allow  for  a  seamless,  and  preferably  lossless  bi-directional  multi-lateral communication  between  the  WSN  as  data  provider  (SOS),  web  clients  as  data  consumers  (SOS)  and  the management system, which interacts with the WSN in a standardised way, too (SOS and SPS). 

2014 NASA International Space Apps Challenge - TETRIS GroupSpace Apps Challenge 2014 - TETRIS Space Suit HUD demo with a Raspberry

As part of the 2014 NASA International Space Apps Challenge I joined an Auckland AUT University Textile Lab group to support their space suit concept idea with some cool wireless video and sensor streaming based on Raspberry Pi.

TETRIS (Terran Expeditionary Technologically Radical Instrumental Suit) is designing a suit, aimed for use by astronauts in space, which will make the astronaut’s work easier and safer to perform. It achieves this by embedding many of the new technologies being released in the recent years into the suit itself in order to: - monitor the astronaut’s life signs and condition via biometric sensors, such as a galvanic sensor for emotions, pulse sensor for the heart rate - allow simple integrated communication via a shoulder mounted camera and microphone - display biometric information to user via projected HUD - take simple electrical readings (when testing/diagnosing equipment) via embedded measurement tools (threaded conductive fabric in gloves) These hardware devices all interface with a RaspberryPi, being used as a central control unit in our design, as well the transceiver for all wireless communications between the astronaut and their remote operations control room.

Link to the 2014 Space Apps project website

The Raspberry Pi video camera live capture was streamed into the remote browser with an overlay of the HUD mockup.

Sources here https://github.com/TetrisGroup/spaceapps