A sensor, comprising: a flexible mounting member comprising an adhesive surface configured to attach directly to a sample and to assume a shape corresponding to at least a portion of the sample when it attaches to the sample; and a plurality of radiation source packages (14a-b, 16a-f) separated from one another and each comprising one or more radiation emitting elements, a spectral detector, and an electronic processor attached to the mounting member, wherein the plurality of radiation source packages (14a-b, 16a-f) comprise multiple long-distance source packages (16a-f) and one or more short-distance source packages (14a-b) relative to the position of the detector, and wherein the electronic processor is configured to: (i) identify an expected spectrum of the sample and/or an expected spectral shape of particular features in the spectrum of the sample, (ii) analyze each of the measured absorbance spectra produced by the multiple long distance source packages (16a-f) to determine a correspondence between expected and measured spectra, (iii) select at least one of the multiple long-distance source packages (16a-f) to direct incident radiation to a subject that produces a measured absorbance spectrum or spectral feature shape that corresponds most closely with the expected spectrum or spectral feature shape of the sample, and (iv) cause the one or more short-distance source packages (14a-b) and the selected long distance source package (16a-f) to direct incident radiation to the subject, to cause the spectral detector to analyze radiation from the subject, and to determine one or more properties of the subject based on the radiation from the subject. a flexible mounting member comprising an adhesive surface configured to attach directly to a sample and to assume a shape corresponding to at least a portion of the sample when it attaches to the sample; and a plurality of radiation source packages (14a-b, 16a-f) separated from one another and each comprising one or more radiation emitting elements, a spectral detector, and an electronic processor attached to the mounting member, wherein the plurality of radiation source packages (14a-b, 16a-f) comprise multiple long-distance source packages (16a-f) and one or more short-distance source packages (14a-b) relative to the position of the detector, and wherein the electronic processor is configured to: (i) identify an expected spectrum of the sample and/or an expected spectral shape of particular features in the spectrum of the sample, (ii) analyze each of the measured absorbance spectra produced by the multiple long distance source packages (16a-f) to determine a correspondence between expected and measured spectra, (iii) select at least one of the multiple long-distance source packages (16a-f) to direct incident radiation to a subject that produces a measured absorbance spectrum or spectral feature shape that corresponds most closely with the expected spectrum or spectral feature shape of the sample, and (iv) cause the one or more short-distance source packages (14a-b) and the selected long distance source package (16a-f) to direct incident radiation to the subject, to cause the spectral detector to analyze radiation from the subject, and to determine one or more properties of the subject based on the radiation from the subject. (i) identify an expected spectrum of the sample and/or an expected spectral shape of particular features in the spectrum of the sample, (ii) analyze each of the measured absorbance spectra produced by the multiple long distance source packages (16a-f) to determine a correspondence between expected and measured spectra, (iii) select at least one of the multiple long-distance source packages (16a-f) to direct incident radiation to a subject that produces a measured absorbance spectrum or spectral feature shape that corresponds most closely with the expected spectrum or spectral feature shape of the sample, and (iv) cause the one or more short-distance source packages (14a-b) and the selected long distance source package (16a-f) to direct incident radiation to the subject, to cause the spectral detector to analyze radiation from the subject, and to determine one or more properties of the subject based on the radiation from the subject.