Ionospheric disturbances affect Global Positioning System (GPS) performance in terms of accuracy and integrity, especially over the equatorial region. During the period of the disturbances, GPS receivers suffer from a high noise level. Not taken into account by the current stochastic model, the ionospheric disturbances degrade GPS positioning accuracy. In addition, non-Gaussian tails are observed in the distribution of the noise during the period of the disturbances; therefore the integrity of GPS can also be affected. This paper develops a statistical solution that is able to mitigate effects of ionospheric disturbances on GPS accuracy and integrity using a commercial dual frequency receiver. The Rate of Total Electron Content (TEC) change Index (ROTI), a parameter derived from the dual frequency receiver, is used to group the levels of ionospheric disturbances. The standard deviations of the pseudorange noise under different groups are evaluated. By incorporating both the ROTI and the satellite elevation, a modified stochastic model is proposed to reduce the effect of the disturbed observation on the positioning accuracy. The performance of the model is evaluated by a test and an inflated sigma for each group is recommended for over-bounding anomalies of observations to protect the user against threats from ionospheric disturbances. This technique, together with results in this paper, can be applied to mitigate the effects of ionospheric disturbances on GPS.

To compare the glycaemic index (GI) of newly developed ‘atta mix’ roti with whole wheat flour roti. Eighteen healthy non-diabetic subjects consumed 50 g available carbohydrate portions of a reference food (glucose) and two test foods (whole wheat flour roti and atta mix roti) in random order after an overnight fast. The reference food was tested on three separate occasions, while the test foods were each tested once. Capillary blood samples were measured from finger-prick samples in fasted subjects ( − 5 and 0 min) and at 15, 30, 45, 60, 90 and 120 min from the start of each food. No significant difference was observed between roti prepared from whole wheat flour and atta mix in terms of appearance, texture, flavour, taste or acceptability. For each test food, the incremental area under the curve and GI values were determined. The GI of atta mix roti (27·3 (sem 2·2)) was considerably lower than the whole wheat flour roti (45·1 (sem 3·5), P < 0·001). Development of foods with lower dietary glycaemic load such as the atta mix roti could help in the prevention and control of diabetes in South Asian populations, which habitually consume very high glycaemic load diets.