Monitoring Vegetation And Erosion Test Sites

It is this high spatial and temporal variability of vegetation, runoff, and erosion patterns which render small-format aerial photography (SFAP) an especially suitable tool for documenting and monitoring them. Hot-air blimp and kite aerial photography (KAP), among other methods, have been employed by JBR, IM, and their groups since 1995 for investigating geomorphological processes and their relationships to vegetation development on areas under extensified land use, mostly abandoned fields and set-aside land in Spain. In particular, six test areas, 24 m x 36 m in size, and their surroundings were intensively monitored in 6-month to 12-month intervals for the EPRODESERT project (Ries et al., 1998; Marzolff, 1999; Ries, 2000), yielding several hundred images at scales between 1:200 and 1:10,000 (areal coverage approximately 35 m to 10 ha).

The image series taken at the test site Maria de Huerva 1 (MDH1, Fig. 16-2) documents the development of

FIGURE 16-2 Time series of the test site Maria de Huerva 1 (MDH1), Province of Zaragoza, Spain. Hot-air blimp photographs by IM and JBR. Field of view ~40 m across. (A) October 1995. (B) April 1996. (C) August 1996. (D) April 1997. (E) April 1998. (F) September 1998.

a former cereal field in the semi-arid Inner Ebro Basin. At the time of the first image (Fig. 16-2A), this field had been set aside as fallow land for five years under the European Union's subsidized set-aside program. The extremely dry period in the preceding years—158 mm precipitation in 1995—kept vegetation cover as low as 7%. Soil sealing and crusting led to sheet and rill erosion and surface runoff coefficients up to 81% (Ries and Hirt, 2008). Clearly visible are the ridges and furrows of the last tillage operation that are dissected by a large rill system in the image center (see also Fig. 10-11).

The following images document the development of the site for the next three years: six months later in April 1996 after a wet winter (Fig. 16-2B); another five months later in August 1996, following a weed-control tillage dictated by the EU set-aside program (Fig. 16-2C); in spring 1997

FIGURE 16-3 Further test sites monitored by the EPRODESERT project in northeastern Spain. Hot-air blimp photographs by IM and JBR. Field of view ~40-60 m across. (A) Maria de Huerva 2, Inner Ebro Basin. (B) Sabayes, Pre-Pyrenees. (C) Bentue de Rasal, Pre-Pyrenees. (D) Arnas, Central Pyrenees. (E) Aisa, High Pyrenees.

FIGURE 16-3 Further test sites monitored by the EPRODESERT project in northeastern Spain. Hot-air blimp photographs by IM and JBR. Field of view ~40-60 m across. (A) Maria de Huerva 2, Inner Ebro Basin. (B) Sabayes, Pre-Pyrenees. (C) Bentue de Rasal, Pre-Pyrenees. (D) Arnas, Central Pyrenees. (E) Aisa, High Pyrenees.

(Fig. 16-2D); one year later in spring 1998 (Fig. 16-2E); and in late summer 1998 (Fig. 16-2F). Note the high spatial concurrence of the images and scale that can be achieved with the hot-air blimp platform in repeated surveys. Similar time series were taken at five further test sites (Fig. 16-3).

Using image-processing and geographic information system (GIS) software for rectification and image analysis, a process-geomorphological information system was developed based on digital georeferenced test area maps with 2.5-cm resolution (Fig. 16-4; Marzolff, 1999, 2003). Visual photo interpretation combined with on-screen digitizing, digital image classification (see Fig. 11-16), and hybrid visual/digital classification methods enabled the detailed mapping of geomorphological processes, density and patterns of vegetation cover, as well as plant life forms. Change maps for vegetation and erosion were created by intersecting operations. Texture and Fourier analysis were employed to delineate automatically micromorphological structures caused by plowing (see Fig. 4-34). After calibration of the cameras, digital elevation models (DEMs) could be generated from stereoscopic images by photogrammetric analysis. The

DEMs with 25-cm resolution were used for computing slope and curvature maps as well as for simulation of potential flow paths over the test areas. Examples for the resulting maps are shown for one monitoring period of the test site MDH1 in Figure 16-5.

Ten months after the soil crusts had been broken by tillage and encouraged by a wet winter, annual herbs and grasses started to recolonize the fallow land, leading to a total coverage of 41% in April 1997 (Fig. 16-5A). The favorable weather conditions continued into the following year, and vegetation cover increased further to 70% until April 1998, predominantly in those areas that had been tilled only superficially. However, the prevalent erosion processes observed on the site could not be suppressed everywhere by the increasing vegetation cover. While sheet wash was stopped or diminished in many areas, one-fifth of the site experienced an intensification of sheet wash (Fig. 16-5D), and 45% of the unchanged area is actually still subject to moderate sheet wash. The spatial change patterns of both vegetation and erosion are remarkably detailed on this site, and contradictory developments often take place in close proximity, although from a perfunctory assessment of the site on a field trip or satellite image

FIGURE 16-4 Flow chart with the main interpretation and processing steps involved in assembling the process-geomorphological information system for the EPRODESERT test sites. Taken from Marzolff (2003, fig. 5).
I I 0 - <5% I I 5 ■ <30% j I 30 - <60% 60 - <90% ■i 90 - 100%

100 - >90 % decrease 90 - >60 % decrease 60 ■ >30 % decrease 30 - >5 % decrease 5 % decrease- <5 % increase 5 - <30 % increase 30 - <60 % increase É0 - <90 % increase 90 - !00 % increase

100 Photography Tips

100 Photography Tips

To begin with your career in photography at the right path, you need to gather more information about it first. Gathering information would provide you guidance on the right steps that you need to take. Researching can be done through the internet, talking to professional photographers, as well as reading some books about the subject. Get all the tips from the pros within this photography ebook.

Get My Free Ebook


Post a comment