A friend of mine (@hazeldickens) recently asked @HayleyEversKing and I; “Can you see the #Jacaranda trees, which bloom every year in #Pretoria, from space?”…#thread (1/n)
For those that have never seen them; #Jacarandas grow all over #Pretoria & #Johannesburg & each year explode in an incredible purple display between September & November. We saw these when we visited @UPTuks in 2011, on an @Access_HP course & they are stunning! (2/n)
We’re not land remote sensing aficionados (ocean please!), but decided to have a look using @CopernicusEU @ESA_EO #Sentinel2 data. We started by comparing a time of year when we know the trees are in bloom (now), with one where we know that weren’t (July) (3/n)
We focussed on the area around @UPTuks after seeing their recent beautiful pictures (bit.ly/2GKHWcC), and sure enough - you can see the purple lined streets in November, but not in July in a natural colour image (the trees are classic green then). (4/n) 
We wanted to see if we could automate this in some way to pick out the #Jacarandas more broadly across the city. We pulled together a *very* rough index using various bands and thresholds using the two images (white spots in image; right panel)(5/n)
Not looking too bad! But this was our 'known' target area…How do other regions look? Let’s check #Johannesburg . The ‘Jacarandex’ implies lots of streets with #Jacarandas and a close look at the natural colour seems to imply its working! (6/n)
Disclaimers; probably lots of false positives in there, so we’d need to look in much more detail at more images, and the spectral characteristics of the #Jacarandas to make it more robust. (7/n)
We’d love to get some local expertise on this. If you are a South African scientist working on #Jacarandas and have some ideas on how we could improve this, we'd love to collaborate! (8/n)
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