Test field and procedure for testing hyperspectral sensors

Abstract

Test field for testing hyperspectral sensors, with - a printable, weatherproof and portable base with a black border, - a plurality of characteristic maps on the substrate, a first characteristic map, wherein the first characteristic map has a colored Siemens star, with at least 36 inwardly tapered wedges, wherein the wedges are white, black and multicolored and a multicolored wedge is always framed by a white and a black wedge and the multicolored wedges have different colors, a second characteristic map, with a plurality of aluminum strips, the aluminum strips consist of aluminum foil, wherein the aluminum strips have the same distance to each other and the strips are arranged next to each other, and are glued to the substrate.

Description

[0001] The invention relates to a test field and a method for testing hyperspectral sensors in flying systems.

[0002] Test patterns for hyperspectral sensors are known from the prior art. Among others, Siemens stars are known as test patterns. A Siemens star can be used to determine the geometric quality of optical sensors. It consists of a circle with alternating white and black circular sectors. The Siemens star can be used to test the quality of an optical imaging system.

[0003] From German patent application DE10 2006 048 767 A1, a device for adjusting and calibrating an infrared system, which is particularly suitable for recording and evaluating thermal images, is known. The device comprises a thermally radiating body in a housing, wherein the surface of the thermally radiating body to be recorded consists of at least two sub-patterns which have different radiation densities in the infrared range and from which a test pattern is formed, such that this test pattern represents differently bright areas in the infrared range.

[0004] The object of the present invention is to enable a simple and quick testing of the quality of a hyperspectral sensor.

[0005] This problem is solved by technical devices according to the independent claims. Technically advantageous embodiments are the subject of the dependent claims, the description, and the drawings.

[0006] According to one aspect, the object of the invention is achieved by a test field for testing hyperspectral sensors, with a weatherproof base, with a first characteristic field on the base, wherein the first characteristic field has a Siemens star, with at least 36 inwardly tapered wedges, wherein the wedges are white, black and colored and a colored wedge is always framed by a white and a black wedge and the colored wedges have different colors, with a second characteristic field on the base, with aluminum strips and the aluminum strips consist of aluminum foil, wherein the aluminum strips have the same distance from each other and the strips are arranged next to each other.

[0007] By applying multiple characteristic maps to the test field's substrate, accelerated, simplified, and more precise quality testing and evaluation of hyperspectral sensors, particularly those of flying systems, can be achieved. The advantage of the solution according to the invention lies in the coordinated or correlated compilation of characteristic maps. In a single process, the properties and capabilities of the hyperspectral sensor can be determined with regard to geometric, radiometric, and spectral image resolution. The substrate is weatherproof and printable. With a weatherproof substrate, the test field can also be used in adverse weather conditions. The substrate could, for example, be a white, printable tarpaulin.

[0008] The first characteristic curve serves to test the visible color spectrum in the wavelength range of 380 nm to 750 nm of the hyperspectral sensor and to test its resolving power. This first characteristic curve therefore features a colored Siemens star, which has inwardly tapered wedges in white, black, and color. It allows the determination of the hyperspectral sensor's image quality with regard to maximum contrast between color and black (no emission) and white (full emission). The colored wedges represent different object colors. The color of an object depends on the proportions that are reflected and absorbed, as well as its illumination. Each colored wedge represents a different object color. Any color from red to violet can be used as the object color for the colored wedges, which thus replicate the color progression of a rainbow.

[0009] The second test field is used to examine the infrared spectrum of the hyperspectral sensor in the wavelength range from 750 nm to 1 mm. For this purpose, strips of aluminum foil are affixed to the weatherproof base of the test field. The aluminum strips are equidistant from each other and have identical dimensions in length and width. The aluminum foil provides thermal radiation reflection, which is detected by the hyperspectral sensor to determine its performance.

[0010] In a technically advantageous embodiment of the test field, the test field features a third characteristic field with rubber strips. The strips are made of rubber and are glued to the substrate, maintaining a uniform distance from one another. Furthermore, the rubber strips have identical dimensions. The rubber strips have the advantage of storing thermal radiation.

[0011] In a further technically advantageous embodiment of the test field, a fourth characteristic map is printed on the substrate. The fourth characteristic map consists of at least four Siemens stars, with the wedges alternating between black and white. The number of black or white wedges is a multiple of 2 n Siemens stars can be used in various configurations, such as 8, 16, 32, and 64 beams. The quality of the modulation transfer function can be directly determined using these different Siemens stars. This also allows for the determination of the -3 dB imaging limit of the hyperspectral sensor.

[0012] In a further technically advantageous embodiment of the test field, a fifth characteristic map is printed on the substrate. This fifth characteristic map consists of a bar in the shape of a rectangle, with the color gradient of a rainbow appearing along its long side. The spectral precision of the hyperspectral sensor can be determined using the color gradient of a rainbow.

[0013] In a further technically advantageous embodiment of the test field, a sixth characteristic field is provided with a gray bar in the form of a rectangle. This gray bar consists of several small rectangles arranged side by side, each small rectangle displaying a shade of gray. Along the long side of the gray bar, the rectangles are sorted from lightest to darkest shades of gray. The radiometric precision of the aerial image sensor can be determined based on these shades of gray.

[0014] In a further technically advantageous embodiment of the test field, a seventh characteristic field with six sub-characteristic fields is provided. The sub-characteristic fields are arranged side by side and each consists of four longitudinal and four transverse strips of the same width and length. The sub-characteristic fields are arranged in descending geometric width, with each sub-characteristic field being reduced in size by 25% compared to the previous one. The seventh characteristic field serves to adjust the direction of movement when the hyperspectral sensor is moved past the test field. The hyperspectral sensor can, for example, be attached to a flying system and fly over the test field. The seventh characteristic field also enables the calculation of the modulation transfer function to determine the image quality of the hyperspectral sensor.

[0015] In another technically advantageous embodiment of the test field, the base has a black frame. The black frame allows for precise placement of the test field in the field and for accurate measurement of its actual size. Furthermore, the black frame enables placement of the test field without distortion.

[0016] The procedure using the test field for testing hyperspectral sensors comprises the following steps: a) Printing the test field base with the printable characteristic curves, b) Performing a hyperspectral measurement of the printed test field to determine a calibrated color spectrum, c) Applying the strips to the base of the test field, d) Transporting and laying out the test field, e) Capturing the test field with the hyperspectral sensor, f) Evaluating the data from the hyperspectral sensor, g) Determining the properties and capabilities of the hyperspectral sensor.

[0017] The test field substrate is printed with the characteristic patterns, for example, using an RGB or CMYK color printer. A spectral measurement of the printed test field is then performed. Since the printed colors may deviate from the defined color values, the spectral measurement of the test field is carried out using the first and second test patterns to obtain a calibrated color spectrum for testing the hyperspectral sensor. Finally, the adhesive strips are applied.

[0018] Exemplary embodiments of the invention are shown in the drawings and are described in more detail below. They show: Fig. 1. The first characteristic curve with a colored Siemens star, where the black and white wedges each frame a colored wedge. The colored wedges are shown in grayscale. Fig. 2 a possible arrangement of the different characteristic curves for a test field. Fig. 3 A simple schematic diagram showing a hyperspectral aerial image sensor on a flying system over a test field.

[0019] Fig. Figure 1 shows the first characteristic curve 10 with a Siemens star, black wedges 11, white wedges 12, and colored wedges 13. The colored wedges 13 are shown in grayscale. Furthermore, the colored wedges 13 are framed by the black and white wedges 11 and 12.

[0020] Fig. Figure 2 shows a test field 1 on a base 80 with a black frame 90 and various characteristic maps. The first characteristic map 10, with the colored Siemens star, is located in the center of test field 1. The second characteristic map 20, with five strips of aluminum foil, is located in the right-hand area. Below the second characteristic map 20, the third characteristic map 30, with three rubber strips, is located. In the corners are Siemens stars of the fourth characteristic map, each with a different number of black and white wedges. Between two Siemens stars in the left part of test field 1 of the fourth characteristic map 40 is the fifth characteristic map 50, with a color bar. This is a rainbow gradient, shown here in shades of gray. The gradient progresses from red at the bottom through yellow to green to blue and ends in violet at the top. In the upper area of ​​test field 1, the gray bar and its small rectangles of the sixth characteristic map 60 are shown.The shades of gray in the small rectangles become progressively darker from left to right. The seventh characteristic map (70) with sub-characteristic maps (71) is located in the lower part of the test field. Six sub-characteristic maps (71) are displayed. These sub-characteristic maps consist of four transverse and four longitudinal stripes. Furthermore, each sub-characteristic map becomes 25% smaller from left to right than the one in front.

[0021] Fig. Figure 3 shows a flying system 100, such as a drone or an aircraft, equipped with a hyperspectral aerial image sensor 110. The hyperspectral aerial image sensor flies over a test field 1. Test field 1 is located in a test area and has been set up accordingly. The flying system 100 flies over the test field 1 to determine the properties and functionality of the hyperspectral aerial image sensor 110.

[0022] The following section describes the procedure in more detail. To test a hyperspectral sensor, such as one mounted on a flying system or a vehicle, characteristic maps are printed onto a test field. Depending on the printer, the respective color matrix must first be measured, as the actual printing specifications do not correspond to the theoretical ones. For this purpose, the printed test field is hyperspectrally measured to obtain a calibrated color spectrum for later evaluation. The characteristic maps are then applied. Depending on the hyperspectral sensor's mounting system, the test field is moved to a test area and laid out there. Alternatively, the test field can be mounted on a frame and then transported to a test area using a vehicle. The hyperspectral sensor then scans the test field.This can be done statically or while driving or flying, depending on the hyperspectral sensor's mounting system. Following the acquisition of data from the test field by the hyperspectral sensor, the captured images can be analyzed to determine the sensor's properties and functionality. Reference sign 1 test field 10 First map 11 Black Wedge 12 White Wedge 13 Colored Wedge 20 Second map 30 Third characteristic field 40 Fourth map 50 Fifth map 60 Sixth map 70 Seventh map 71 Sub-characteristic field 80 support 90 frames 100 Flying System 110 Hyperspectral Sensor

Claims

[1] Test field for testing hyperspectral sensors, with - a printable, weatherproof and portable base with a black frame, - a plurality of characteristic diagrams on the base, a first characteristic diagram, the first characteristic diagram having a colored Siemens star, with at least 36 inwardly tapered wedges, the wedges being white, black and colored and a colored wedge always being framed by a white and a black wedge and the colored wedges having different colors, a second characteristic diagram, with a plurality of aluminum strips, the aluminum strips consisting of aluminum foil, the aluminum strips being the same distance from one another and the strips being arranged next to one another, and being glued to the base. [2] Test field according to claim 1, with a further characteristic field, a third characteristic field, with a plurality of rubber strips, these rubber strips consist of rubber and these are arranged next to each other at the same distance from each other. [3] Test field according to one of the preceding claims, with a further characteristic field, a fourth characteristic field, with at least four Siemens stars, wherein the respective Siemens stars have alternating black and white wedges, each Siemens star has a different number of wedges, wherein the number of wedges is always a multiple of 2 n is. [4] Test field according to one of the preceding claims, with a further characteristic field, a fifth characteristic field, with a color bar in rectangular shape in color, with a color gradient of a rainbow. [5] Test field according to one of the preceding claims, with a further characteristic field, a sixth characteristic field, that the sixth characteristic field consists of a gray bar, the gray bar has a rectangular shape and consists of small rectangles arranged next to one another, these small rectangles have different gray levels. [6] Test field according to one of the preceding claims, with a further test field, a seventh characteristic map, the seventh characteristic map consisting of six sub-characteristic maps, wherein a sub-characteristic map always has four transverse and four longitudinal strips of the same width and height, the sub-characteristic maps are arranged next to one another and the sub-characteristic maps become 25% smaller in length and width than the previous sub-characteristic map. [7] Method with a test field according to one of the preceding claims, the method comprising the following steps: a) printing at least one printable map on the substrate, b) Carrying out a hyperspectral measurement of the printed first characteristic map, c) Applying the second map with aluminum strips to the base, d) Moving and aligning the test field, e) Detection of the test field by the hyperspectral sensor, f) Evaluating the data from the hyperspectral sensor, g) Determining the quality of the hyperspectral sensor in a single process according to geometric, radiometric and spectral quality of image resolution.

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