Satellite-based trophic index for the integration of small and medium-sized lakes into the trophic state monitoring in Brandenburg, Germany

Sa elli e-based ophic index o he in eg a ion o small and medium-sized lakes in o he ophic
s a e moni o ing in B andenbu g, Ge many
Zamzow, M.; Ma zinge , A.; Bas in, L.
The ophic index is o en used o moni o he p ima y p oduc ion o lakes. In B andenbu g,
Ge many, lakes a e sampled se e al imes e e y h ee yea s be ween Ap il and Oc obe . The ophic
index is hen calcula ed om he alues o phospho us concen a ion, u bidi y and chlo ophyll-a
con en . This is usually only done o lakes ha a e moni o ed acco ding o he Wa e F amewo k
Di ec i e (a ea > 50 ha). The low empo al esolu ion in combina ion wi h na u al annual a ia ions
makes end analysis o ophic le els e y di icul and a high p opo ion o lakes a e excluded om
his moni o ing.
Sa elli e images can be used o ob ain in o ma ion on chlo ophyll-a and u bidi y. Phospho us, as a
nu ien o algae, also has an indi ec e ec on wa e colo . The e a e al eady many indices based on
he Cope nicus Sen inel-2 p og am, such as he No malized Di e ence Chlo ophyll Index, which can
be used o eal- ime wa e moni o ing. In addi ion, annual da a a e essen ial o lake managemen
o iden i y long- e m ends. The ophic index is a widely used and easily in e p e ed indica o in his
ega d.
The AD4GD p ojec explo ed i) which bands o he Sen inel-2 images a e bes sui ed o es ima ing
ophic s a e, ii) how he da a can be empo ally agg ega ed wi hin a season, and iii) whe he one
pixel wi hin a lake is su icien o eliably desc ibe he ophic s a e o he lake. Especially he la e
was necessa y o apply he me hod o small lakes whe e egula moni o ing is no a ailable.
The de eloped No malized Di e ence T ophic Index (NDTI), agg ega ed o e he mon hs o Ap il o
Oc obe , bes ep esen ed he ophic index based on measu ed alues. I was de eloped and
alida ed using 294 lakes in B andenbu g wi h ophic da a be ween 2018 and 2022 and is de ined
o a sa elli e image as
𝑁𝐷𝑇𝐼𝑖𝑚𝑎𝑔𝑒 =𝐵5 − 𝐵2
𝐵5 + 𝐵2
Band 5 desc ibes he nea in a ed e lec ance a 705 nm, band 2 he e lec ance o blue ligh a 490
nm. In oligo ophic lakes, band 2 e lec ance usually domina es and he index is below ze o. The
ophic index based on in-si u measu emen s is bes calcula ed om mon hly alues. Simila ly,
NDTIimage is i s a e aged mon hly and hen seasonally (Ap il o Oc obe in Ge many).
The esul ing NDTIseason was ound o be highly co ela ed wi h he in-si u da a o he a ailable yea s
(Pea son co ela ion coe icien be ween 0.83 and 0.92). Thus, i allows a compa ison o he ophic
s a e o lakes in he B andenbu g egion. The da a a e a ailable a an annual esolu ion, which is
h ee imes mo e equen han he con en ional analysis. This allows a much mo e eliable end
analysis, which can be used o moni o he success o wa e quali y imp o emen measu es o o
iden i y wa e quali y p oblems mo e quickly. Small lakes can be included in he moni o ing wi hou
much e o .
A i s sensi i e analysis has shown ha he classi ica ion o eu ophic wa e bodies is mo e eliable
han ha o oligo ophic wa e bodies. Fu he ac o s in luencing he accu acy o he me hod will be
in es iga ed in a subsequen sensi i i y analysis.