Multifunctional Sky Camera System for Total Sky Imaging and Spectral Radiance Measurement

• US 20140327769A1
• Filed: 09/19/2013
• Published: 11/06/2014
• Est. Priority Date: 04/30/2013
• Status: Active Grant

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Hamann, Hendrik F., Lu, Ziyuan
• Granted Patent: US 9,781,363 B2
• Time in Patent Office: Days
• US Class Current: 348/144
• CPC Class Codes: G01W 1/12 Sunshine duration recorders measuring intensity of sunshine G01J
• CPC Class Codes: G06T 2207/10021 Stereoscopic video; Stereoscopic image sequence
• CPC Class Codes: G06T 5/94 based on local image properties, e.g. for local contrast enhancement
• CPC Class Codes: G06T 7/20 Analysis of motion motion estimation for coding, decoding, compressing or decompressing digital video signals H04N19/43, H04N19/51
• CPC Class Codes: G06T 7/215 Motion-based segmentation
• CPC Class Codes: G06T 7/593 from stereo images
• CPC Class Codes: G06T 7/85 Stereo camera calibration
• CPC Class Codes: H04N 13/239 using two 2D image sensors having a relative position equal to or related to the interocular distance H04N13/243 takes precedence
• CPC Class Codes: H04N 23/60 Control of cameras or camera modules
• CPC Class Codes: H04N 23/69 Control of means for changing angle of the field of view, e.g. optical zoom objectives or electronic zooming
• CPC Class Codes: H04N 23/698 for achieving an enlarged field of view, e.g. panoramic image capture
• CPC Class Codes: H04N 23/75 by influencing optical camera components
• CPC Class Codes: H04N 25/621 for the control of blooming

Abstract

A multifunctional sky camera system and techniques for the use thereof for total sky imaging and spectral irradiance/radiance measurement are provided. In one aspect, a sky camera system is provided. The sky camera system includes an objective lens having a field of view of greater than about 170 degrees; a spatial light modulator at an image plane of the objective lens, wherein the spatial light modulator is configured to attenuate light from objects in images captured by the objective lens; a semiconductor image sensor; and one or more relay lens configured to project the images from the spatial light modulator to the semiconductor image sensor. Techniques for use of the one or more of the sky camera systems for optical flow based cloud tracking and three-dimensional cloud analysis are also provided.

Claims

1. A sky camera system, comprising:

an objective lens having a field of view of greater than about 170 degrees;

a spatial light modulator at an image plane of the objective lens, wherein the spatial light modulator is configured to attenuate light from objects in images captured by the objective lens;

a semiconductor image sensor; and

one or more relay lens configured to project the images from the spatial light modulator to the semiconductor image sensor.

2. The sky camera system of claim 1, wherein the objective lens comprises a fish eye lens.

3. The sky camera system of claim 1, wherein the spatial light modulator comprises a liquid crystal modulator, a quantum well modulator, or a micro-blinds based modulator.

4. The sky camera system of claim 1, wherein the semiconductor image sensor comprises a charge-coupled device (CCD) sensor or a complementary metal-oxide semiconductor (CMOS) sensor.

5. The sky camera system of claim 1, wherein the semiconductor image sensor comprises an anti-blooming CCD sensor or an anti-blooming CMOS sensor.

6. The sky camera system of claim 1, wherein the semiconductor image sensor comprises a sensor covering from about 400 nm to about 1,100 nm spectral region.

7. The sky camera system of claim 1, further comprising:

a spectral filtering component between the objective lens and the semiconductor image sensor configured to switch between desired wavelength windows.

8. The sky camera system of claim 7, wherein the spectral filtering component comprises electrochromatic glass, liquid crystal, or acousto-optical grating.

9. The sky camera system of claim 1, wherein the semiconductor image sensor has been calibrated.

10. A total sky imaging system, comprising:

at least one first sky camera system and at least one second sky camera system, wherein the first sky camera system and the second sky camera system each includes (i) an objective lens having a field of view of greater than about 170 degrees, (ii) a spatial light modulator at an image plane of the objective lens, wherein the spatial light modulator is configured to attenuate light from objects in images captured by the objective lens, (iii) a semiconductor image sensor, and (iv) one or more relay lens configured to project the images from the spatial light modulator to the semiconductor image sensor, and

wherein the first sky camera system and the second sky camera system are located at a distance of from about 100 meters to about 1,000 meters from one another.

11. The total sky imaging system of claim 10, wherein the first sky camera system and the second sky camera system each further includes (v) a spectral filtering component between the objective lens and the semiconductor image sensor configured to switch between desired wavelength windows.

12. An apparatus for cloud tracking, the apparatus comprising:

a memory; and

at least one processor device, coupled to the memory, operative to;

(a) obtain a time-lapsed series of sky images using a sky camera system including (i) an objective lens having a field of view of greater than about 170 degrees, (ii) a spatial light modulator at an image plane of the objective lens, wherein the spatial light modulator is configured to attenuate light from objects in images captured by the objective lens, (iii) a semiconductor image sensor, and (iv) one or more relay lens configured to project the images from the spatial light modulator to the semiconductor image sensor; and

(b) compute a velocity of one or more pixels in the time-lapsed series of sky images using optical flow analysis, wherein pixels in the time-lapsed series of sky images corresponding to cloud regions have a finite velocity and pixels in the time-lapsed series of sky images corresponding to non-cloud regions have a zero velocity.

13. The apparatus of claim 12, wherein the at least one processor device is further operative to:

(c) distinguish the cloud regions from the non-cloud regions in the time-lapsed series of sky images using the velocity of the pixels computed in step (b) and a location of the pixels in the time-lapsed series of sky images.

14. The apparatus of claim 12, wherein the at least one processor device is further operative to:

(d) forecast cloud movement using linear extrapolation and the velocity of the pixels computed in step (b) wherein the pixels corresponding to the cloud regions at location (x,y) at time t are forecasted to be at location (x+V_xΔ

t, y+V_yΔ

t).