Feature/glossary updates (#72)

* updated dataset maturity guide

* typo fix

* Fix quotation marks and update provisional use advice

* fixing typos

* add python to code block

docs/guides/about/glossary.md

@@ -48,6 +48,13 @@ In the context of remote sensing, algorithms generally specify how to determine
 lower-level source data. For example, algorithms prescribe how atmospheric temperature and moisture profiles are 
 determined from a set of radiation observations originally sensed by satellite sounding instruments.
 
+{#ancillary}
+## Ancillary datasets
+
+Data which enhance processing and utilisation of remote sensing instrument data. Ancillary datasets are used to assist
+in the analysis and classification of e.g. [ARD](#ard) by providing supporting data on conditions at the time of 
+satellite data acquisition, such as aerosol and water vapour concentrations. 
+
 {#aws}
 ## Amazon Web Services (AWS)
 
@@ -159,7 +166,7 @@ and the most up-to-date collection available.
 The reproduction of the [collection](#collection), including all downstream products, with the 
 initial input being the rawest form ([telemetry](#telemetry)). Collections are updated when 
 there are fundamental changes and upgrades to the data suite that make it incompatible with the existing collection. 
-Therefore a collection upgrade is more akin to a movie franchise reboot than a re-release.
+Therefore, a collection upgrade is more akin to a movie franchise reboot than a re-release.
 
 {#ceos-seo}
 ## Committee on Earth Observations, Systems Engineering Office (CEOS-SEO)
@@ -268,6 +275,14 @@ capability. The ESA is a partner of the [Copernicus Programme](#cop-prog).
 
 The angle between a ray reflected from a surface and the line perpendicular to the surface at the point of emergence.
 
+{#final}
+## Final
+
+A stage in DEA's dataset maturity lifecycle. DEA’s best quality [ARD](#ard), produced using high quality [ancillary](#ancillary) 
+datasets derived from observed data.
+
+For more information, see [DEA dataset maturity](/guides/reference/dataset_maturity_guide#final).
+
 {#fc}
 ## Fractional Cover (FC)
 
@@ -303,7 +318,7 @@ For more information, see [Geoscience Australia](https://www.ga.gov.au/).
 ## Geomedian
 
 Geometric median is a robust high-dimensional statistic that maintains relationships between spectral bands, while 
-producing a multi-dimensional median over a timeseries of satellite images.
+producing a multidimensional median over a timeseries of satellite images.
 
 The Geometric Median provides information on the general conditions of a landscape over a timeseries.
 
@@ -338,6 +353,15 @@ a typical desktop computer or workstation in order to solve large problems in sc
 
 The angle between a ray incident on a surface and the line perpendicular to the surface at the point of incidence.
 
+{#interim}
+## Interim
+
+A stage in DEA's dataset maturity lifecycle. Interim production means that one or more [ancillary](#ancillary) datasets were not 
+available at the time of production, and the dataset has instead been corrected using a combination of [NRT](#nrt) 
+climatological ancillaries, and [final](#final) observed ancillaries.
+
+For more information, see [DEA dataset maturity](/guides/reference/dataset_maturity_guide#interim).
+
 {#nidem}
 ## Intertidal Elevation
 
@@ -474,12 +498,12 @@ Radiation just beyond the visible light spectrum. In Landsat and Sentinel 2 Eart
 radiation between 0.7 - 0.9 micrometers.
 
 {#nrt}
-## Near-real time (NRT)
+## Near real-time (NRT)
 
-NRT data is a less refined/calibrated dataset, which is available much sooner after satellite acquisition than standard 
-[ARD](#ard) data.
+A stage in DEA's dataset maturity lifecycle. NRT data is a less refined/calibrated dataset, which is available much 
+sooner after satellite acquisition than standard [ARD](#ard) data.
 
-For more information, see [DEA dataset maturity](/guides/reference/dataset_maturity_guide/).
+For more information, see [DEA dataset maturity](/guides/reference/dataset_maturity_guide#nrt).
 
 {#odc}
 ## Open Data Cube (ODC)
@@ -562,7 +586,7 @@ definition which contains the product description and specification.
 ## Python
 
 The programming language used to develop the [Open Data Cube](#odc) and most of [Digital Earth Australia](#dea). 
-It is an easy to use language, which also provides simple access to high performance processing capabilities.
+It is an easy-to-use language, which also provides simple access to high performance processing capabilities.
 
 For more information, see [Python](https://www.python.org/).
 
@@ -758,7 +782,7 @@ For more information, see [NASA Thematic Mapper Plus](https://landsat.gsfc.nasa.
 {#thredds}
 ## Thematic Real-time Environmental Distributed Data Services (THREDDS)
 
-An National Computational Infrastructure ([NCI](#nci)) server, which is a high-performance and high-availability 
+A National Computational Infrastructure ([NCI](#nci)) server, which is a high-performance and high-availability 
 installation of Unidata's Thematic Real-time Environmental Distributed Data Services (THREDDS).
 
 THREDDS serves many of NCI’s open data collections at the file level, as well as some aggregations. It provides many 
@@ -844,13 +868,13 @@ For more information, see [NASA: World Reference System](https://landsat.gsfc.na
 {#xarray}
 ## xarray
 
-An open source project and [Python](#python) package for working with labelled multi-dimensional arrays such as those 
+An open source project and [Python](#python) package for working with labelled multidimensional arrays such as those 
 returned by the [Open Data Cube](#odc).
 
 {#yaml}
 ## Yet Another Markup Language (YAML)
 
-A human readable data storage format. It is used throughout [DEA](#dea) for metadata files, product definitions and 
+A human-readable data storage format. It is used throughout [DEA](#dea) for metadata files, product definitions and 
 other configuration files.
 
 {#zenith}

docs/guides/reference/dataset_maturity_guide.md

@@ -0,0 +1,114 @@
+# DEA Dataset Maturity
+
+In December 2022, DEA implemented **dataset maturity** levels to provide a more streamlined user 
+experience and access mechanism for DEA Analysis Ready Data ([ARD](/guides/about/glossary/#ard)) datasets. All ARD data for a single sensor is now 
+provided in a single product, streamlining the user experience and minimising the data handling required by users. 
+
+As higher quality corrections become available, they replace the rapid near real-time data within the same product. 
+This upgrade provides users a simplified experience whereby they now only need to connect to one data feed which 
+provides the best possible, most up-to-date information at any point in time.
+
+Dataset maturity metadata attributes are currently implemented across all Sentinel 2 and Landsat Collection 3 ARD products. 
+
+## How does 'dataset maturity' work?
+
+DEA produces ARD data to three maturity levels: 
+* **Near Real-Time (NRT)**
+* **Interim**
+* **Final**
+
+{#nrt}
+### Near Real-Time (NRT)
+
+**Near Real-Time (NRT)** is a rapid ARD product produced within 48 hours of image capture. NRT 
+data is corrected using existing long term climatology data, rather than observed conditions on the day of the 
+satellite capture (because these observational datasets, called [ancillaries](/guides/about/glossary/#ancillary), take a few weeks to be received by DEA). Due to the use of average
+condition data, rather than observational data to perform the corrections to produce ARD, NRT data can be published 
+quickly, however is considered to be of slightly lower quality than '**final**' ARD data.
+
+Over the next few weeks, higher quality ancillary datasets become available describing the specific 
+atmospheric conditions at the time and location the satellite image was captured. Using these 
+ancillaries, ‘**final**’ maturity ARD is produced. This replaces the '**NRT**' or '**interim**' product (see below).  
+
+{#final}
+### Final
+
+**Final** ARD is DEA’s best quality ARD, produced using high quality ancillary datasets derived 
+from observed data. These ancillary datasets are slower to produce but are observational 
+datasets of the conditions at the time of image capture and so provide our most accurate dataset 
+corrections. 
+
+DEA uses the following dynamic ancillary datasets to produce its **final** ARD:
+* Bidirectional reflectance distribution function ([BRDF](/guides/about/glossary/#brdf)) data from the United States Geological Survey 
+* Water Vapour from USA National Oceanographic and Atmospheric Administration
+
+{#interim}
+### Interim
+
+If high quality ancillaries required for the **final** ARD model don’t become available **within 23 days** of image capture,
+‘**interim**’ maturity data is produced as a *stand-in* until the full ancillaries are available to produce the ‘**final**’ version.
+This is our fall-back until the issue is resolved.
+
+**Interim** production means that one or more ancillary datasets were not available at the time of production, and the dataset has 
+instead been corrected using a combination of **NRT** climatological ancillaries, and **final** observed 
+ancillaries. If there are no delays in the ancillary datasets, then **interim** maturity is skipped and 
+datasets move directly from **NRT** to **final**.
+
+## Dataset maturity flowchart
+
+All three maturity levels can be present inside a single product, with the maturity information stored 
+in the product metadata and as part of the filename, enabling users to choose an appropriate dataset 
+maturity level to suit their requirements. Datasets with lower maturity level will be replaced by more 
+mature dataset versions (interim and final) as they are generated. 
+
+![dataset_maturity_flowchart](/_files/reference/dataset_maturity_flowchart.drawio.svg)
+
+**Tip:** to view larger, right-click then select **open image in new tab**
+
+% Diagram editing notes for internal use:
+% The SVG above contains an embedded copy of the source used to generate it.
+% Download it, then drop it into https://app.diagrams.net/ to edit. 
+% When finished, *save* it, OR use *export as SVG* with the **Include a copy of my diagram** option checked.
+% Then commit it back to the repo.
+
+## How is this different from what DEA used to do? 
+
+Previously, DEA produced two separate products: 
+
+* Near Real-Time, which was kept as a rolling 90 day archive; 
+* ARD, published 9 to 16 days after satellite acquisition. 
+
+The user was then able to select which product they wanted to use according to their purpose. 
+It was more difficult to combine products as both NRT and the final ARD product contained data 
+for the same time step.  
+
+## How do I load only Near Real-Time/Interim/Final data using the datacube? 
+
+DEA data can be filtered to specific dataset maturity levels using `dataset_maturity` 
+metadata field. Valid options are 'final', 'nrt' or 'interim'; for example, 
+to load only 'final' maturity Landsat 8 data
+
+```python
+import datacube
+dc = datacube.Datacube()
+
+dc.load(product="ga_ls8c_ard_3",
+        measurements=['nbart_red'],
+        x=(150, 150.1),
+        y=(-30, -30.1),
+        time=('2022-01', '2022-02'),
+        dataset_maturity="final")
+```
+
+{#provisional}
+## What about provisional?
+
+The term **provisional** is used by DEA to denote products or services that have not yet passed quality control, and/or
+have not yet been finalised for release. Products or services tagged as provisional could be e.g. beta versions 
+of new products, could represent other stages of product development, or could not yet have passed 
+DEA's quality control standards for a product or service. 
+
+**Provisional products are available for use, but should be used with appropriate caution.** See the individual product 
+or service metadata pages for information on product limitations and use. 
+
+Once a product is formally released, it is renamed to remove the provisional tag.