Most smartphones have a built-in GNSS receiver, which can calculate its position based on observations of signals transmitted by at least four visible satellites. Most smartphone GNSS receivers are single frequency, which means they can obtain information transmitted within a certain set of wavelengths (from 1.1-1.6 GHz). Using this single-frequency information from at least four satellites to pinpoint the location will result in a spatial accuracy of around 10 m on average for most smartphones. Of course, the more satellites that are used to derive the position, the better the position estimates will be.
Accessing this raw GNSS data has also been made possible through the development of application interfaces in newer versions of the Android operating system, released since 2017. The CAMALIOT app uses these application interfaces to collect and extract the raw GNSS data received by a smartphone. Hence, the app only operates on Android version 7 or later, but it can collect the raw GNSS data from Android phones that have either single-frequency or dual-frequency receivers.
However, some newer models of Android phones are equipped with dual-frequency GNSS receivers; see the list of available phones here
. This means that these smartphone models can receive additional information from the GNSS satellites across a wider set of frequencies, where this added information can produce a higher positional accuracy.
Ionospheric disturbances negatively affect the positional accuracy of single-frequency GNSS-capable devices, like most smartphones. In order to overcome this, users need external information to correct the ionospheric signal delay, e.g., by using external ionospheric models. Global empirical ionospheric models already exist that allow the signal delay to be predicted in the form of the total electron content (TEC). TEC is a function of many variables, including long and short-term changes in the solar ionizing flux, magnetic activity, the season, the time of day, the location and the viewing direction.
Obtaining VTEC with higher precision, better spatial and temporal resolution and taking rapid disturbances such as geomagnetic storms into account is one of the objectives of the CAMALIOT project. In addition to improving space weather forecasting, the models can also be used to improve the estimates of the position of the GNSS receiver.
TEC parameters are estimated from rudimentary assumptions and mapping functions that relate slant TEC observations to TEC in the vertical direction, hereafter referred to as VTEC. However, accurate ionospheric forecasts are limited, to a large extent, by the disturbances induced by geomagnetic storms or other rapid events. Such phenomena cannot be easily accounted for in conventional prediction models.
Yes, you can use the app to collect data at your location and download it in RINEX3 format. Click on the cloud icon at the bottom of the app. This allows you to download data from individual logging sessions.
In the future, you will be able to access the data collected by others from the GSSC portal