--- title: Correlation with Solar Zenith Angle description: Understand how EKO Q uses solar zenith angle analysis to identify data consistency patterns, time shifts, orientation issues, and reference data limitations. --- [![EKO Q](https://eko-support.eko-instruments.com/hs-fs/hubfs/EKO%20Q%20Logo%201-2.png?height=75&width=248&name=EKO+Q+Logo+1-2.png)](https://eko-support.eko-instruments.com/knowledge-base?hsLang=en) EU | A | あ ⌄ English Deutsch Português Español [EKO website](https://eko-instruments.com) [EKO Q](https://eko-q.eko-instruments.com) [Contact us](https://share-eu1.hsforms.com/1MNfi6yWgQ6ab174lgwH9XA2eqp93) Search # How can we help you? Your browser does not support the video tag. [Skip to content](https://eko-support.eko-instruments.com/knowledge-base/correlation-with-solar-zenith-angle#main-content) English Show submenu for translations ![EKO Q Logo 1-2](https://eko-support.eko-instruments.com/hs-fs/hubfs/EKO%20Q%20Logo%201-2.png?width=248&height=75&name=EKO%20Q%20Logo%201-2.png) Open main navigation Close main navigation - English Show submenu for translations - [Contact us](https://share-eu1.hsforms.com/1MNfi6yWgQ6ab174lgwH9XA2eqp93) [Contact us](https://share-eu1.hsforms.com/1MNfi6yWgQ6ab174lgwH9XA2eqp93) How can we help you? - There are no suggestions because the search field is empty. 1. [Knowledge base](https://eko-support.eko-instruments.com/knowledge-base?hsLang=en) 2. [Understand reports and plots](https://eko-support.eko-instruments.com/knowledge-base/understand-reports-and-plots?hsLang=en) 3. [Detailed Report and plots](https://eko-support.eko-instruments.com/knowledge-base/understand-reports-and-plots?hsLang=en#detailed-report-and-plots) # Correlation with Solar Zenith Angle The deviation between the measurement data and reliable reference data, analysed as a function of solar zenith angle, provides a unique perspective on data consistency. The plots in this section are particularly useful for detecting subtle effects in the data after overall agreement has been verified. Depending on the dataset used, this comparison can help identify: - limitations of irradiance models at low solar elevation angles, - small time shifts, - sensor orientation mismatches, - pyranometer cosine response effects, - and other potential issues. The plots show the absolute irradiance difference between the two datasets on the Y-axis, plotted against the solar zenith angle corresponding to each data timestamp on the X-axis. Separate plots are provided for: - data filtered for clear-sky conditions, and - data representing all-sky conditions. ![](https://eko-support.eko-instruments.com/hs-fs/hubfs/image-png-Jul-21-2026-08-15-29-1917-AM.png?width=1244&height=475&name=image-png-Jul-21-2026-08-15-29-1917-AM.png) Please note that these plots do not directly characterise directional response or other specific sensor properties. They should be used as a starting point for further investigation. ### Typical patterns **1. Mostly straight horizontal line around the zero baseline** ![](https://eko-support.eko-instruments.com/hs-fs/hubfs/image-png-Jul-21-2026-08-16-58-6836-AM.png?width=1413&height=536&name=image-png-Jul-21-2026-08-16-58-6836-AM.png) This is the expected pattern for healthy data. Small variations around the baseline in the clear-sky plot, together with scatter up to approximately 200 W/m² in the all-sky plot, generally reflect the expected limitations of the reference irradiance model. **2. Thin inclined line** ![](https://eko-support.eko-instruments.com/hs-fs/hubfs/image-png-Jul-21-2026-08-17-47-9395-AM.png?width=1015&height=394&name=image-png-Jul-21-2026-08-17-47-9395-AM.png) When comparing a well-maintained sensor to a reference instrument, this pattern may indicate a mismatch in instrument calibration and/or directional response. Further investigation is required before drawing conclusions. Review the insights provided in other sections, particularly [***General Linearity***](https://eko-support.eko-instruments.com/knowledge-base/general-linearity?hsLang=en), and consult a trusted expert if necessary. **3. Split pattern at higher zenith angles** ![](https://eko-support.eko-instruments.com/hs-fs/hubfs/image-png-May-29-2026-02-48-54-9965-PM.png?width=670&height=269&name=image-png-May-29-2026-02-48-54-9965-PM.png) A small but systematic overestimation or underestimation at low solar elevations is typically associated with a slight time shift or a similar issue. The shift may be small enough for the Time Shift test to pass, while still appearing as a result of: - timestamp inaccuracies, - data processing errors, - or inconsistencies in the reference data. Further investigation is recommended to determine whether corrective action is necessary. **4. Circular patterns or highly scattered data** **![](https://eko-support.eko-instruments.com/hs-fs/hubfs/image-png-May-29-2026-02-54-04-5642-PM.png?width=670&height=264&name=image-png-May-29-2026-02-54-04-5642-PM.png)** This pattern is typically caused by significant mismatches related to time zone configuration, site location, sensor orientation, or other fundamental setup parameters. These issues are usually also visible in other analyses, such as ***[Time Shift](https://eko-support.eko-instruments.com/knowledge-base/time-shift-detailed-report?hsLang=en)*** and [**Sensor Orientation**](https://eko-support.eko-instruments.com/knowledge-base/orientation-test-detailed-report?hsLang=en). Major configuration issues should be resolved before relying on the solar zenith angle analysis. ### **Final note** This analysis should be used as a pattern-recognition tool, not as a standalone diagnosis. Any deviations should be reviewed together with other report sections, especially General Linearity, Time Shift, and Sensor Orientation, before drawing conclusions or taking corrective action. Angle-dependent deviations may sometimes be influenced by shading or site obstructions. For related checks, see [**Nearby Shading**](https://eko-support.eko-instruments.com/knowledge-base/shading-impact-detailed-report?hsLang=en). - [Start here](https://eko-support.eko-instruments.com/knowledge-base/start-here?hsLang=en) - [Set up your EKO Q workspace](https://eko-support.eko-instruments.com/knowledge-base/set-up-your-eko-q-workspace?hsLang=en) - [Import and check data](https://eko-support.eko-instruments.com/knowledge-base/import-and-check-data?hsLang=en) - [Run analysis](https://eko-support.eko-instruments.com/knowledge-base/run-analysis?hsLang=en) - [Understand reports and plots](https://eko-support.eko-instruments.com/knowledge-base/understand-reports-and-plots?hsLang=en#main-content) - [Report overview](https://eko-support.eko-instruments.com/knowledge-base/understand-reports-and-plots?hsLang=en#report-overview) - [Test Summary](https://eko-support.eko-instruments.com/knowledge-base/understand-reports-and-plots?hsLang=en#test-summary) - [Detailed Report and plots](https://eko-support.eko-instruments.com/knowledge-base/understand-reports-and-plots?hsLang=en#detailed-report-and-plots) - [Troubleshooting and limits](https://eko-support.eko-instruments.com/knowledge-base/troubleshooting-and-limits?hsLang=en#main-content) - [Upload troubleshooting](https://eko-support.eko-instruments.com/knowledge-base/troubleshooting-and-limits?hsLang=en#upload-troubleshooting) - [Plans, limits, and coverage](https://eko-support.eko-instruments.com/knowledge-base/troubleshooting-and-limits?hsLang=en#plans-limits-and-coverage) [![Logo\_primary logo+tagline\_email size\_RGB](https://eko-support.eko-instruments.com/hs-fs/hubfs/Logo_primary%20logo+tagline_email%20size_RGB.png?width=194&height=43&name=Logo_primary%20logo+tagline_email%20size_RGB.png "Logo_primary logo+tagline_email size_RGB")](http://eko-instruments.com) [eko-instruments.com](https://eko-instruments.com/) Copyright © 2025, eu.eko-instruments.com ![EKO Instruments](https://eko-instruments.com/wp-content/uploads/2024/05/EKO-footer-logo.svg) ## Contact & Customer Support - E: eko-q@eko-instruments.com Certificates: ![ASTM certificate](https://eko-instruments.com/wp-content/uploads/2025/10/astm-cert.svg) ![ISO certificate](https://eko-instruments.com/wp-content/uploads/2025/10/iso-cert.svg) ![IEC certificate](https://eko-instruments.com/wp-content/uploads/2025/10/iec-cert.svg) ![HMEI certificate](https://eko-instruments.com/wp-content/uploads/2025/10/hmei-cert.svg) © 2026 EKO Instruments Co., Ltd. All rights reserved Follow us [in](https://www.linkedin.com/company/eko-instruments) [f](https://www.facebook.com/ekoinstruments/) [▶](https://www.youtube.com/channel/UCdY-w-KMXxal6IsOXqc3gLQ)