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Albedo: A Reflectance App

Version 1.1

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Albedo: A Reflectance App

Thomas Leeuw

Utilities, Education

IOS
GBP 0.00


Download Albedo: A Reflectance App on the Appstore





Albedo is an app designed to measure the albedo (or reflectance) of a surface. Albedo is simply defined as the ratio of light reflected from a surface to the light incident upon the surface. The albedo of a surface can be easily interpreted as the percent of incident light reflected by the surface (e.g. Albedo of fresh snow ~ 90%; Albedo of asphalt ~ 10%). The Albedo app is able to measure both the broadband albedo (across the entire visible spectrum) and the spectral albedo in the red, green, and blue color channels of camera.

IMPORTANT: Albedo requires the use of an 18% photographers gray card as a reference. Gray cards are widely available at photography shops and online. Visit the supporting website for more information on gray cards.

Albedo has an easy to use interface that guides users through the collection of two images: a gray card image and an image of any surface. After the images are collected they can be analyzed immediately. In the analysis of the images, the Albedo app calculates the albedo of the surface in the RGB color channels of the camera. The data is instantly saved and can be accessed again via the Albedo app or downloaded onto a computer from Albedo's data folder (accessible through iTunes).

How it works:

Albedo uses the camera as simple light sensor (photometer). Relative light intensity can be measured by normalizing the camera pixel values by the exposure. Therefore, the three color channels of the camera (RGB: Red, Green, Blue) provide a measure of light intensity in three regions of the visible spectrum.

The light intensity reflected from the surface is measured when the user captures an image of the surface. This is normalized by the ambient illumination using the gray card image. The final product is a nearly illumination independent measure of the surface albedo. Surface albedo is an important parameter used by environmental scientist to understand how different surfaces and substances interact with light. Albedo is commonly used in climatology, astronomy, and geoengineering.



Release notes


Fixes Camera Permission Bug



Albedo: A Reflectance App screenshot oneAlbedo: A Reflectance App screenshot twoAlbedo: A Reflectance App screenshot threeAlbedo: A Reflectance App screenshot four


The Developer Thomas Leeuw also wrote the apps listed below, click the icon to visit the pages.

HydroColor: Water Quality App
HydroColor: Water Quality App

Free
HydroColor is a water quality application that uses the iPhone camera to determine the reflectance of natural water bodies. Using this information, HydroColor can estimate water turbidity (0-80 NTU), concentration of suspended particulate matter (SPM) (g/m^3) and the backscattering coefficient in the red (1/m). IMPORTANT: HydroColor requires the use of an 18% photographers gray card as a reference. Gray cards are widely available at photography shops and online. Visit the supporting website for more information on gray cards.

HydroColor has an easy to use interface that guides users through the collection of three images: a gray card image, a sky image, and a water image. To ensure the best results, HydroColor taps into the iPhone’s GPS, gyroscope, and compass to aid users in the collection of these images. After images are collected they can be analyzed immediately. In the analysis of the images, HydroColor calculates the reflectance of the water body in the RGB color channels of the camera. It then uses the reflectance values to determine the turbidity of the water in NTU (nephelometric turbidity units).

The data is instantly saved and can be accessed again via HydroColor or downloaded onto a computer from the documents folder (accessible in iTunes). The text file contains additional information about the measurement including: latitude, longitude, date, time, sun zenith, sun azimuth, phone heading, phone pitch, exposure values, RGB reflectance, and turbidity. Additional water quality parameters (e.g. chlorophyll concentration) will be added to HydroColor as research continues. Proceeds from HydroColor will go toward developing additional algorithms for HydroColor and to creating additional Apps like HydroColor.

How it works:

HydroColor uses the iPhone camera as simple light sensor (photometer). Relative light intensity can be measured by normalizing the camera pixel values by the exposure. Therefore, the three color channels of the camera (RGB: Red, Green, Blue) provide a measure of light intensity in three regions of the visible spectrum.

The light intensity measured in the water image is corrected for sky reflection off the surface (using the sky image). The corrected water image provides the intensity and color of light emanating from the water. This is normalized by the ambient illumination using the gray card image. The final product is a nearly illumination independent measure of the water’s reflectance, known as remote sensing reflectance. In oceanography, satellites are used to calculate the same product (remote sensing reflectance) from space.

The reflectance is directly related to the amount and type of suspended particles in the water. An increase in turbidly (i.e. suspended sediments) will cause greater scattering of light and increase the overall reflectance of the water. Particles containing pigments, such as phytoplankton (algae), will absorb light in specific regions of the visible spectrum. Thus, pigment containing particles can be detected by comparing the relative reflectance in the RGB channels....
Albedo: A Reflectance App
Albedo: A Reflectance App

Free
Albedo is an app designed to measure the albedo (or reflectance) of a surface. Albedo is simply defined as the ratio of light reflected from a surface to the light incident upon the surface. The albedo of a surface can be easily interpreted as the percent of incident light reflected by the surface (e.g. Albedo of fresh snow ~ 90%; Albedo of asphalt ~ 10%). The Albedo app is able to measure both the broadband albedo (across the entire visible spectrum) and the spectral albedo in the red, green, and blue color channels of camera.

IMPORTANT: Albedo requires the use of an 18% photographers gray card as a reference. Gray cards are widely available at photography shops and online. Visit the supporting website for more information on gray cards.

Albedo has an easy to use interface that guides users through the collection of two images: a gray card image and an image of any surface. After the images are collected they can be analyzed immediately. In the analysis of the images, the Albedo app calculates the albedo of the surface in the RGB color channels of the camera. The data is instantly saved and can be accessed again via the Albedo app or downloaded onto a computer from Albedo's data folder (accessible through iTunes).

How it works:

Albedo uses the camera as simple light sensor (photometer). Relative light intensity can be measured by normalizing the camera pixel values by the exposure. Therefore, the three color channels of the camera (RGB: Red, Green, Blue) provide a measure of light intensity in three regions of the visible spectrum.

The light intensity reflected from the surface is measured when the user captures an image of the surface. This is normalized by the ambient illumination using the gray card image. The final product is a nearly illumination independent measure of the surface albedo. Surface albedo is an important parameter used by environmental scientist to understand how different surfaces and substances interact with light. Albedo is commonly used in climatology, astronomy, and geoengineering....