# Comparing Monitoring Networks to Assess Urban Heat Islands in Smart Cities
## 5 Analysis of the Measurement Data
### Data Quality Control  
A data quality control is performed in two stages. The first takes into account the details of the hourly urban climatic databases [101; 102] and of the AWSs [103; 104]. Successive control processes are then followed:  
* Selection of AWSs according to the amount of data, discarding those that do not reach at least 80% (a smaller percentage is considered insufficient to characterize the period). * Verification of the temperature range for the period in question, which is set from 11 \({}^{\circ}\)C to 47 \({}^{\circ}\)C (corresponding to \(\pm\)6 \({}^{\circ}\)C with respect to the absolute minimum and maximum temperatures registered by the city's AEMET station in the month of August 2024, 17 \({}^{\circ}\)C and 41 \({}^{\circ}\)C, respectively [105]). * Checking the consistency of the readings for the same value continuously, fixing as outliers those hourly values repeated over 5 consecutive hours. * Searching for sudden or significant changes between consecutive time marks, defining as outliers those hourly registers with variations above 12 \({}^{\circ}\)C with respect to the previous one (to maintain the stability and relevance of the data, ensuring coherent data and eliminating the infrequent sudden changes that are usually due to extreme phenomena or measuring errors). * Checking the validity of the continuity of the data in between observations and the average of the remaining AWS, fixing a threshold of four standard deviations (guaranteeing the detection of really extreme values, eliminating extremely rare values possibly due to measuring errors or real anomalies, while also minimizing the elimination of legitimate data). * Checking the daily oscillation in temperatures, eliminating those registers of the days in which the said oscillation is lower than 9 \({}^{\circ}\)C (minimum value of thermal oscillation registered by the AEMET in the city in the period in question). * Checking sensor aging, devices with a total uncertainty exceeding \(\pm\)0.5 \({}^{\circ}\)C were excluded, while those with an accumulated LTD above \(\pm\)0.3 \({}^{\circ}\)C were critically reviewed. As a result, three situations were identified: no evidence of aging in the Bs network; a lack of knowledge for WU network sensors; and a cumulative LTD of \(\pm\)0.39 \({}^{\circ}\)C for devices \"h\" and \"i\" in the Nt network; however, these are not associated with any control points or analysis zones, and are therefore of limited relevance to the study. Thus, following the data quality control performed in this first stage, 20 AWSs of Bs with 12144 registers (97.3% of those available) are maintained, as are 10 AWSs of Nt with 6075 registers (97.4% of the total) and nine AWSs of WU, with 5597 registers (99.7% of the total). In the second stage of the control, and based on the now clean registers, the similarities of the two sets of data between the networks are evaluated with respect to the following questions:  
* The probability distribution and density of the registers from each AWS, according to different temperature ranges (Figure 7): it can be seen that the registers of the AWSs of Bs and WU are uniformly distributed between the different levels, which happens with those of the AEMET, with similar mean values (29.5 \(\pm\) 0.4 \({}^{\circ}\)C in Bs and WU and 29.4 \({}^{\circ}\)C in AEMET) and quartiles (first 25.2 \(\pm\) 0.6 \({}^{\circ}\)C and second 34.4 \(\pm\) 0.6 \({}^{\circ}\)C in Bs and WU and 25.2 and 34.5 \({}^{\circ}\)C in AEMET). However, those of the Nt show a great heterogeneity (mean 29.5 \(\pm\) 1.1 \({}^{\circ}\)C, first quartile 25.9 \(\pm\) 1.2 \({}^{\circ}\)C, and second quartile 34.8 \(\pm\) 1.9 \({}^{\circ}\)C). The differences between the amplitude of data registered in the AWSs of the different networks are similarly worth noting, while Bs and WU show 3.7 \({}^{\circ}\)C (from 20.1 to 23.8 \({}^{\circ}\)C) and 6.7 \({}^{\circ}\)C (from 19.7 to 26.4 \({}^{\circ}\)C), respectively; Nt registers 8.7 \({}^{\circ}\)C (from 18.2 to 26.9 \({}^{\circ}\)C).