Collecting in situ remote sensing reflectances of submersed macrophytes to build up a spectral library for lake monitoring

Abstract

To map the aquatic vegetation of Bavarian (Germany) freshwater lakes in a large-scaled and quick way, remote sensing is a helpful tool. For interpretation of the data, a spectral library of different macrophyte and sediment reflectances is under development. Therefore, multi-temporal in situ remote sensing reflectances were sampled from May to October 2011 with hyperspectral RAMSES spectroradiometers. Occurring spectral variations during the growing season could be linked to biometric and phenological data of the particulate species. Principal component analyses showed that, by applying the presented method, differentiation of the macrophytes from sediment and among each other is possible and can be improved by multi-temporal data.

Seasonal Variation in Spectral Response of Submerged Aquatic Macrophytes: A Case Study at Lake Starnberg (Germany)

“…The effect of sediment quality on macrophyte growth [21][22][23] was beyond the scope of this study, mainly because the same patches were analyzed for both years. A previous study by Wolf et al [13] already demonstrated the phenologic pattern changes within the growing season. However, that study did not link spectral patterns with temperature effects and it did not apply a modeling approach for phenologic and seasonal comparisons.…”

“…Remote sensing offers a timeand cost-effective method to support monitoring approaches including those recommended by the WFD. Due to its capability to deliver information at high spatiotemporal resolution, remote sensing methods offer the potential to observe detailed seasonal changes in macrophyte distribution and water quality [11][12][13][14][15][16][17][18][19]. It can complement hitherto in-situ data collection along transects by divers and is suggested for closing the gap between the snapshots of in-situ mappings of the WFD [10,20].…”

“…At the beginning of the growing season, the spectral response, even of sparsely vegetated areas, is sediment-dominated. Organic material on the lake bottom such as epiphytes and detritus may alter the spectral response of bare sediment [6,13,[39][40][41]. During the growing season, changes in macrophyte/sediment coverage ratio, leaf size and orientation, leaf pigment concentrations and cellular structure specifically influence intensity and shape of spectral signatures [6,13,40].…”

“…The maximum in macrophyte bottom coverage and biomass content heralds the senescence phase. During this period, the spectral signature is affected by degrading Chlorophyll a (Chl-a) content in ageing leaves [42,43] and the change of canopy structure by collapsed macrophytes [6,13]. Knowledge about the development pattern of the investigated macrophyte species during the growing season is required for the envisaged differentiation on species level by means of remote sensing [13,15].…”

“…Pinnel [38] and Wolf et al [13] analyzed in-situ spectral signatures of various submersed macrophyte species (Chara spp., Elodea nuttallii, Najas marina, and Potamogeton perfoliatus) in different lakes in the Alpine foreland to detect spectral variations during the growing season. From these studies [13,38], we learn that the phenologic development within the year and the related spectral signatures are species-specific and deliver a phenologic fingerprint, an approach successful applied in forestry for forest tree species identification, if recorded continuously [45,46].…”