Time Reference Check
- Zuzana Bielčiková
General overview
Use the Time reference check tool for identification and correction of time shifts, time drifts and other time-related issues based on testing diurnal symmetry - morning vs. afternoon (in kt/h0 space). The time reference is critical for all subsequent quality tests, such as calculated solar geometry (position of sun). Moreover, the correct time reference is a basic prerequisite for the comparison of data sources from different datasets. After correction of time-related issues, the operator saves all required time corrections and the quality status of the dataset is updated.
The user can manually identify the shifts by diurnal symmetry test - morning vs. afternoon (in kt/h0 space). The second option is to run auto-detection, which automatically suggests the location and value of shifts and drifts in the data. The detected shifts can be manually modified or deleted. The detection runs from a few seconds to a few minutes depending on the volume of data. The automatic recognition identifies these shifts within the recognition uncertainty. Always select the original data if you would like to shift the data manually.
Component | Description |
Times series graph | Line graph of original records, records after shifting, and clear-sky. Lines is possible to switch off by clicking on the legend (without pan or zoom tool) |
Graph tools | Tools: Reset original view, Back to the previous view, Forward to next view, Pan, Zoom, Edit plot, Edit axis, curve and image parameters, Save the figure. Pan tool is able to use as a zoom tool by right click. |
Kt graphs | Graphs show diurnal symmetry (morning vs afternoon) of original and shifted data |
Shift overview graph | Line graph showing detected shifts in the dataset with uncertainty. The data are broken into segments, each segment has a uniform shift and its uncertainty. |
Dataset | Input dataset for Time reference check |
Column | Input column for Time reference check. The detection of time shifts is only based on this column. It must be either GHI or GTI type column. |
Time shifts arrow | Shows/hides the list of existing shifts |
Existing shifts | List of existing shifts |
New shifts | List of new shifts. You can disable time shift by checkbox. After running the auto-detection, the shift is shown with its uncertainty. The color shows the confidence of detected shift: green - high, yellow - medium, red - low. |
Auto-detection | Runs the automatic shift recognition. |
Import | Opens time shifts importer. You can choose another dataset and import time shifts from them. |
New | Creates a new shift. It is possible to create a new shift by selecting the time span in Time series graph (pan and zoom tools must be disabled). |
Remove | Deletes shift |
Reorder | Reorder time shifts from lowest to highest time stamp. |
Time from | Datetime setting the beginning of the span. |
Reset min | Resets datetime field to minimum possible value. |
Time to | Datetime setting the end of the span. |
Reset max | Resets datetime field to maximum possible value. |
Time shifts | Sets time shift value |
Draw kt diagrams only for the active shift | Allows you to display all records or only records from the actual time shift span. |
Redraw graphs | Redraws graphs by actual shifts and settings |
Settings | Opens settings window consisting of marker size setting and marker transparency setting for kt plots. |
Save | Saves changes |
Final save | Saves changes and QC status “TIME_REFERENCE_CHECK” will be assign to the dataset. |
Save as | Saves changes into the copy of dataset and QC status “TIME_REFERENCE_CHECK” will be assign to the dataset. |
Close | Closes window |
Limitations
Limitation | Probability | Severity |
Shift error compared to manual shifting is usually around 2 minutes | high | low |
The smallest possible recognizable shift can be between 0.5 and 1 minute depending on shift postprocessing. | - | - |
This method is suitable only for GHI and GTI measurements, It cannot be performed on DNI. | - | - |
The shift correction is based on selected radiation within the dataset and all columns have the same correction. Shift correction of each column separately is not allowed. | - | - |
This method uses postprocessing which unifies shifts through the dataset. Running the detection after shifting for the second time can give small non-zero shifts because of the applied postprocessing. | medium | low |
There can be no shift computation for a non-complete day (part of a day missing). Also, it can happen for a full day but surrounded by days of missing values. | low | high |
The computed shift for a corrupted day measurement has a larger error. By corrupted it means:
| medium | medium |
The time shift is computed for the whole day. We cannot correct the shift that happened in the middle of the day. | low | high |
The time shift is in some cases not computed (set to zero). It can happen when there are only missing values or invalid values during the day. | medium | low |