*Article* **Easily Implemented Methods of Radiometric Corrections for Hyperspectral–UAV—Application to Guianese Equatorial Mudbanks Colonized by Pioneer Mangroves**

**Marion Jaud 1,2,\*, Guillaume Sicot 3, Guillaume Brunier 4, Emma Michaud 4, Nicolas Le Dantec 1,2, Jérôme Ammann 2, Philippe Grandjean 5, Patrick Launeau 6, Gérard Thouzeau 4, Jules Fleury <sup>7</sup> and Christophe Delacourt <sup>2</sup>**

	- F-29280 Plouzané, France; jerome.ammann@univ-brest.fr (J.A.); christophe.delacourt@univ-brest.fr (C.D.) <sup>3</sup> ENSTA Bretagne, M3 Team-Lab-STICC—UMR CNRS 6285, 2 rue François Verny, F-29200 Brest, France;
	- guillaume.sicot@ensta-bretagne.fr <sup>4</sup> CNRS, University Brest, IRD, Ifremer, LEMAR, F-29280 Plouzané, France; guillaume\_brunier@hotmail.fr (G.B.); emma.michaud@univ-brest.fr (E.M.); gerard.thouzeau@univ-brest.fr (G.T.)
	- <sup>5</sup> Laboratoire de Géologie de Lyon: Terre, Planètes, Environnement-UMR 5276, University Lyon, Université Claude Bernard Lyon 1, ENS Lyon, CNRS, F-69622 Villeurbanne, France; philippe.grandjean@univ-lyon1.fr
	- <sup>6</sup> Laboratoire de Planétologie et Géodynamique—UMR 6112, University Nantes, 2 Chemin de la Houssinière, F-44300 Nantes, France; patrick.launeau@univ-nantes.fr
	- <sup>7</sup> CEREGE—UMR 7330, University Aix Marseille, CNRS, IRD, INRA, Collège de France, F-13545 Aix-en-Provence, France; fleury@cerege.fr
	- **\*** Correspondence: marion.jaud@univ-brest.fr; Tel.: +33-298498891

**Abstract:** Hyper-DRELIO (Hyperspectral DRone for Environmental and LIttoral Observations) is a custom, mini-UAV (unmanned aerial vehicle) platform (<20 kg), equipped with a light push broom hyperspectral sensor combined with a navigation module measuring position and orientation. Because of the particularities of UAV surveys (low flight altitude, small spatial scale, and high resolution), dedicated pre-processing methods have to be developed when reconstructing hyperspectral imagery. This article presents light, easy-implementation, in situ methods, using only two Spectralon® and a field spectrometer, allowing performance of an initial calibration of the sensor in order to correct "vignetting effects" and a field standardization to convert digital numbers (DN) collected by the hyperspectral camera to reflectance, taking into account the time-varying illumination conditions. Radiometric corrections are applied to a subset of a dataset collected above mudflats colonized by pioneer mangroves in French Guiana. The efficiency of the radiometric corrections is assessed by comparing spectra from Hyper-DRELIO imagery to in situ spectrometer measurements above the intertidal benthic biofilm and mangroves. The shapes of the spectra were consistent, and the spectral angle mapper (SAM) distance was 0.039 above the benthic biofilm and 0.159 above the mangroves. These preliminary results provide new perspectives for quantifying and mapping the benthic biofilm and mangroves at the scale of the Guianese intertidal mudbanks system, given their importance in the coastal food webs, biogeochemical cycles, and the sediment stabilization.

**Keywords:** drone; hyperspectral imaging; radiometric calibration; reflectance; pioneer mangroves; intertidal sediments
