diff --git a/NumericalData/CDPP-AMDA/OMNI/omni-hour-all.xml b/NumericalData/CDPP-AMDA/OMNI/omni-hour-all.xml
index 50326b9..e9e05f6 100644
--- a/NumericalData/CDPP-AMDA/OMNI/omni-hour-all.xml
+++ b/NumericalData/CDPP-AMDA/OMNI/omni-hour-all.xml
@@ -26,6 +26,11 @@ for creating the OMNI data set.</Acknowledgement>
                 <URL>http://omniweb.sci.gsfc.nasa.gov/html/ow_data.html</URL>
                 <Description>Extensive OMNI documentation pages</Description>
             </InformationURL>
+            <InformationURL>
+                <Name>Matzka, J., Stolle, C., Yamazaki, Y., Bronkalla, O., and Morschhauser, A. (2021). The geomagnetic Kp index and derived indices of geomagnetic activity. Space Weather, 19, e2020SW002641.</Name>
+                <URL>https://doi.org/10.1029/2020SW002641</URL>
+                <Description/>
+            </InformationURL>
         </ResourceHeader>
         <AccessInformation>
             <RepositoryID>spase://SMWG/Repository/CNES/CDPP-AMDA</RepositoryID>
@@ -220,6 +225,7 @@ for creating the OMNI data set.</Acknowledgement>
         <Parameter>
             <Name>Kp index</Name>
             <ParameterKey>omni_kp</ParameterKey>
+            <Description>The standard Kp values look like 0, 0+, 1-, 1, 1+, 2-, ... but are stored as Kp = 0, 3, 7, 10, 13, 17, ... in the OMNI data set. We have mapped 0+ to 3, 1- to 7, 1 to 10, 1+ to 13, 2- to 17, etc.</Description>
             <Ucd>meta.code;phys.magField</Ucd>
             <RenderingHints>
                 <DisplayType>TimeSeries</DisplayType>
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