Recent changes to the various solar data products provided by the Bureau are summarised below. However, changes to individual observations which occur as part of the Bureau's ongoing quality control process are not listed. See also Updates to One Minute Solar Data. Please read the Bureau's Disclaimer which is relevant to this information.
An attempt has been made to broadly classify the change in terms of an estimated magnitude of the change. However, it is your responsibility to review this information to determine the significance and impact for your work.
Please contact us if you require further information about these changes.
The gridded hourly global horizontal irradiance (GHI) and direct normal irradiance (DNI) dataset has been updated to include data to the end of October 2016. The associated GHI metadata and DNI metadata have been revised to include new observations provided from the Japanese Himawari 8 satellite.
Enhancements have been made to the full dataset of gridded hourly global solar irradiance (GHI) and gridded hourly direct normal solar irradiance (DNI). These enhancements include the provision of 24 grids per day (up from 18); night time values no longer indicated as missing values; and improved correction of data to remove bias errors associated with the conversion from satellite image to irradiance value. Previously, the Bureau product code IDCJAD0111 refered to both data sets combined. From this point there will be a unique code for each parameter: IDCJAD0026 for gridded Hourly Global Solar Irradiance, and IDCJAD0027 for gridded Hourly Direct Normal Solar Irradiance.
A number of changes have been made to the dataset to improve accuracy and useablity of the data. These are described below, and in the IDCJAD0026 GHI metadata and IDCJAD0027 DNI metadata documents.
The Bureau's ground solar data undergo a number of quality assurance tests, and are occasionally reprocessed as testing techniques are improved. Observations from the Darwin site covering the period January to July 2007 have been reprocessed after a fault in the tracking equipment was detected. Furthermore, during this period earthing issues with the global pyranometer were also detected and removed.
Hourly grids of global solar irradiance (GHI) and direct normal solar irradiance (DNI) across Australia are provided by a computer model which analyses satellite images. High quality observations from the Bureau's ground stations are subsequently used to fine-tune these estimates (bias correction). A bug in the software used to generate these data prevented the bias correction from being applied to observations covering the period between Jan 01, 2013 and Sep 30, 2014. The affected global and direct normal solar irradiance data (product IDCJAD0111) have been updated with the appropriate bias correction.
The solar irradiance values produced raw from the Bureau's satellite data processing have a substantial bias, as determined from comparisons with surface-based irradiance measurements from the Bureau's radiation network. This bias is modelled as a function of irradiance and solar zenith angle, and is used to adjust the satellite estimates to improve agreement with the ground observations.
The bias correction varies with the values of irradiance and solar zenith angle. For GHI the bias correction results in a moderate reduction and most strongly affects the lower values. The change is amplified for DNI, for which it most strongly affects the middle values. To get an overall measure of the change in the corrected data after the bias correction was applied, the hourly data were integrated into daily exposures, then averaged over the affected period. The mean daily global horizontal exposure without the bias correction was, compared to the bias corrected data, 6-10% high over most of the country, except up to 19% in coastal NSW, southern Victoria and Tasmania. The mean daily direct normal exposure without the bias correction was 15-30% high, except up to 40% in southern Victoria and northern Cape York, and up to 50% in Tasmania.
Download the updated hourly gridded global and direct normal solar irradiance data for the affected 21 month period (4 compressed files, 5 Gbyte in total). This free update will only be available until 30th June 2015. The data will be superceded by an enhanced version of the entire gridded solar data set which will be available at normal cost recovery pricing.
The satellite-derived daily solar exposures for September 2013 to June 2014 (2013-09-01 to 2014-06-30) have been updated using a new bias correction based on surface-based exposure measurements.
One of the steps in the production of the satellite-derived daily solar exposures is an adjustment to reduce biases with respect to observations from the Bureau's high quality ground stations. The ground data are available only after a delay of up to several months due to the partially manual nature of their quality control. Thus, the initial bias correction of the daily satellite data cannot be done against the corresponding ground data. Instead, for near-real-time production the bias model is based on a temporal extrapolation of previous satellite-to-ground comparisons. At a later date, a more effective routine bias adjustment is done once the relevant ground data become available.
The daily global solar exposure data accessed via Climate Data Online and also available as gridded data are provided by a computer model which analyses satellite images. High quality observations from the Bureau's ground stations are used to fine-tune these solar exposure data. The information used for fine-tuning the computer model data needs to be updated periodically. However, there was a delay in this updating process which led to a less effective adjustment for model bias. The daily global solar exposure data (products IDCJAC0016 and IDCJAC0003) have been updated and made available via Climate Data Online from 3 April 2014.
The daily solar exposures produced raw from the Bureau's satellite data processing have a substantial exposure-dependent bias, as determined from comparisons with surface-based exposure measurements from the Bureau's radiation network. This bias can be modelled as a linear function of exposure, with the model coefficients changing on a time scale of months for a given satellite, and this model can be used to adjust the satellite exposures. The surface-based measurements are available only after a delay of several months due to the partially manual nature of their quality control. Thus the near-real-time satellite exposures must be adjusted with a temporal extrapolation of the bias model.
The temporal extrapolation of the bias model should be updated periodically as new surface-based observations come in, so that the extrapolation is not too far ahead. However, a prolonged delay between updates reduced the effectiveness of the bias adjustment process, particularly in the early summer period (see Figure Data-difference for an example). The raw exposures have been processed with a refreshed bias model derived from the surface observations, and made available via Climate Data Online from 3 April 2014.
The change in exposure value between before and after the revision will vary linearly with exposure.
Download the updated daily gridded global solar exposure data for the affected period (340 Mbyte, compressed). This free update will only be available until 30th June 2015. The data will be superceded by an enhanced version of the entire gridded solar data set which will be available at normal cost recovery pricing.
In previous data updates affecting all stations and years, the Minimum 1 second direct irradiance (over 1 minute) values in each data file were instead the Maximum 1 second direct irradiance (over 1 minute) statistics for the same time period. The Maximum 1 second (over 1 minute) statistics are correct and duplicated across both fields. As this duplication occurred when the database was created, it will be necessary to reprocess all relevant data, a task which will take a substantial period of time to complete. Please note that as of this data update, the Minimum 1 second direct irradiance (over 1 minute) values have been replaced with blanks. Users will be notified via RSS feed when the updated data becomes available.
The Bureau's solar instruments are regularly calibrated by comparison to a pair of reference pyrheliometers, which are in turn traceable to the National Radiometric Standards. This quality assurance process detected a change in the sensitivity of the Bureau's reference instruments. As a consequence, the sensitivities of field instruments derived from these references at the Darwin site (014015) have been updated. Global and diffuse irradiance data have been reprocessed using the updated sensitivities, with changes within 4% of the originally released values. The period in question is from 27 May 2009 until 28 May 2013. In addition, approximately four weeks of global and diffuse data between 11 Dec 2006 and 24 Apr 2007 have been removed after additional information has revealed that a suspected lightning strike adversely affected instrumentation at the Darwin site.
Uncertainties for nighttime longwave irradiance have now been added where previously unavailable. Additional quality control of some historical observations may have occured since the last release.
Eight new or re-established ground monitoring stations have been funded for a period of eighteen months through a collaborative project between Geoscience Australia and the Bureau, as part of the Australian Government Solar Flagships Program funded by the Australian Renewable Energy Agency. The primary goal for expanding the network is to provide valuable additional data to help enhance the computer model which generates the satellite-derived solar exposure provided by the Bureau and through Geoscience Australia. The data from these stations will also be publicly available via the Bureau's One Minute Solar Data product.