A sensor array for use in a hollow elongate housing having a continuously tapered outer wall and inner wall internally tapered and having a larger maximum outer diameter at a first end compared to the maximum outer diameter of a second end for use in the ground, wherein the sensor array element includes: a carrier sheet (40, 40a, 40b, 40c) of flexible material, wherein the carrier sheet (40, 40a, 40b, 40c) has four edges, wherein the carrier sheet (40, 40a, 40b, 40c) has at least two pairs (42, 44) of electrically conductive regions lying between an first edge and a second edge of the carrier sheet (40, 40a, 40b, and 40c), wherein the carrier sheet comprises fixing elements and is configured to be formed and fixed, using the fixing elements, into a shape for insertion into the elongate hollow housing, wherein the two electrically conductive regions (42, 44) of a pair of electrically conductive regions are shaped and located near enough each other such that when the carrier sheet (40, 40a, 40b, 40c) is formed and fixed into said shape, the pair of electrically conductive regions (42, 44) form a capacitive element, characterized in that at least one pair of opposite edges of the carrier sheet is non-parallel, and in that adjacent pairs of capacitive elements (42 and 44) have a different diameter, each usable to sense at least the moisture content of the ground surrounding the location of the capacitive element located within the elongate hollow housing, and in that at least one of the fixing elements includes a tang formed by the shape of the flexible material of the carrier sheet (40, 40a, 40b, 40c) being suitable for insertion into a slot (54a, 54b, 54c, 54d) in the carrier sheet and for resisting extraction from the slot in the carrier sheet. a carrier sheet (40, 40a, 40b, 40c) of flexible material, wherein the carrier sheet (40, 40a, 40b, 40c) has four edges, wherein the carrier sheet (40, 40a, 40b, 40c) has at least two pairs (42, 44) of electrically conductive regions lying between an first edge and a second edge of the carrier sheet (40, 40a, 40b, and 40c), wherein the carrier sheet comprises fixing elements and is configured to be formed and fixed, using the fixing elements, into a shape for insertion into the elongate hollow housing, wherein the two electrically conductive regions (42, 44) of a pair of electrically conductive regions are shaped and located near enough each other such that when the carrier sheet (40, 40a, 40b, 40c) is formed and fixed into said shape, the pair of electrically conductive regions (42, 44) form a capacitive element, characterized in that at least one pair of opposite edges of the carrier sheet is non-parallel, and in that adjacent pairs of capacitive elements (42 and 44) have a different diameter, each usable to sense at least the moisture content of the ground surrounding the location of the capacitive element located within the elongate hollow housing, and in that at least one of the fixing elements includes a tang formed by the shape of the flexible material of the carrier sheet (40, 40a, 40b, 40c) being suitable for insertion into a slot (54a, 54b, 54c, 54d) in the carrier sheet and for resisting extraction from the slot in the carrier sheet.