Combined airborne thermography and visible-to-near infrared reflectance measurement for soil moisture mapping

Abstract

We first present a review of the so-called triangle/trapezoid method for soil moisture evaluation from optical remote sensing data obtained in the red, near infrared and thermal infrared bands. Recent improvements based on additional vegetation indexes obtained for example from multiwavelength signals in SWIR band will also be presented. In a second part we describe the results we obtained for this purpose by using a microbolometer camera onboard of a motorglider. Signal processing for atmosphere correction and orthorectification was specifically developed for this application. First results on the path for identification of soil water content with this approach will be presented.

Leak Detection in Water Transmission Systems by Multispectral Remote Sensing With Airplane and UAV

“…This method consists in combining the apparent temperature and a vegetation index like NDVI to perform a temperature-NDVI scatterplot for all the pixels over an area with a wide diversity in terms of cover fraction and water content. The name is related to the (roughly) triangle shape of the obtained scatterplot [13][14][15][16][17][18][19][20][21]. The vertex of the triangle is often truncated, giving a trapezoidal shape.…”

“…The vertex of the triangle is often truncated, giving a trapezoidal shape. The scatterplot yields to the calculation of a water index for each point or pixel by making a quotient between its relative position with respect to the dry edge and the wet edge of the triangle/trapezoid [13,15,[18][19][20][21].…”

Multispectral Approach Assessment for Detection of Losses in Water Transmission Systems by Airborne Remote Sensing

“…It consists in combining the apparent temperature and a vegetation index like NDVI. When plotting the temperature and the NDVI for all pixels over an area presenting a broad diversity both in cover fraction and in humidity, a scatterplot with a roughly triangular shape is obtained, whence the name: the Triangle Method [10][11][12][13][14][15][16][17][18][19][20][21][22]. Note that the vertex of the triangle is often truncated, giving a trapezoidal shape.…”

“…More involved approaches consist in using a SVAT model (Soil Vegetation Atmosphere Transfer) in combination with the triangular scatterplot [11,13,15]. Recent works considered a supplementary parameter or index (albedo [16][17][18] or CAI-Cellulose Absorption Index [17][18]) in order to remove ambiguities appearing when both soil and vegetation experience large reflectance variations. Most of the time, the Triangle/trapezoid method has been applied to satellite images, hence providing soil moisture maps at low resolution (100-500m) [12][13][14].…”

“…Most of the time, the Triangle/trapezoid method has been applied to satellite images, hence providing soil moisture maps at low resolution (100-500m) [12][13][14]. Applications to airborne remote sensing data for getting information on moisture at a higher resolution (1-5m) are less common [15,[17][18][19][20][21][22]. They actually reveal higher difficulties, one of them being the surface heterogeneity exacerbated by the higher resolution sensors; as a consequence, it imposes a higher demand on the accuracy of the image registration process.…”